Linear Infrastructure Overbuild Guide by Bill Price & Nigel Fraser

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Linear Infrastructure Overbuild Guide Edited by Bill Price and Nigel Fraser




Šbuildoffsite2019 ISBN: 978-0-86017-935-1

British Library Cataloguing and Publication Data A catalogue record is available for this publication from the British Library. Published by Buildoffsite, CIRIA, Griffin Court, 15 Long Lane, London EC1A 9PN. This publication is designed to provide accurate and authoritative information on the subject matter covered. It is sold and/or distributed with the understanding that neither the authors nor the publisher are thereby engaged in rendering a specific legal or any other professional service. While every effort has been made to ensure the accuracy and completeness of the publication, no warranty or fitness is provided or implied and the authors and publisher shall not have, neither liability nor responsibility to any person or entity with respect to any loss or damage arising from its use. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, including photocopying and recording without the written permission of the copyright holder, application for which should be addressed to the publisher. Such written permission must also be obtained before any part of this publication is stored in a retrieval system of any nature. If you would like to reproduce any part of the figures, text or technical information from this or any other CIRIA publication for use in other documents or publications, please contact CIRIA Publishing for more details on copyright terms and charges at or tel. 020 7549 3300 Commissioned by: Buildoffsite Edited and project managed by: Bill Price and Nigel Fraser Proof reading and literary review by: Lauren Fraser Typeset and design by: Sara Kotsani



Buildoffsite is a membership organisation with members from a wide range of UK and international client, supply, professional services and academic organisations. Buildoffsite is a UK-based business organisation that promotes: • • • • • •

Increased use of offsite methods across all sectors of the UK construction market; Innovation in the development of offsite solutions; More effective promotion of business and project benefits by offsite solution suppliers; Improved understanding by clients and suppliers of the benefits of offsite solutions; Education and skills development in the use of offsite solutions; Debate, discussion and knowledge transfer relating to the use of offsite solutions.

Mission Buildoffsite’s mission is to be the trusted, independent voice of the UK construction industry with respect to offsite and pre-manufacturing, and to provide all relevant support to our members and other stakeholders to enable them to feel confident to promote and adopt the same. Vision A permanent, positive, transformation of the UK construction industry – enabled through the increased adoption of offsite and pre-manufactured solutions to drive increased productivity.

CIRIA The Construction Industry Research Information Association is the organisation that underpins the Buildoffsite organisation.


About the editors

Bill Price Bill Price is a director at WSP and a structural engineer by background. His career has included buildings and structures across many sectors, usually delivering multidisciplinary engineering services. He was responsible for the early design development stages of the Shard and associated with all the projects at London Bridge, helping to raise the profile of tall buildings in London, especially around transport nodes. In 2016 Bill co-edited ‘A Strategic Design Guide to Tall Buildings’ for the British Council for Offices, published by the RIBA. Since 2012 Bill has been closely associated with the delivery and thought leadership around rail overbuild. Bill authored and led the production of the WSP papers ‘Building our way out of a crisis’, ‘Out of Thin Air: Building Above London’s Rail Lines’ and ‘Out of Thin Air: One Year On’. He has presented on the topic at many conferences and events in the UK, continental Europe and Australia.

Nigel Fraser Nigel Fraser was one of the founders of Buildoffsite when working at BAA. His background is multi-disciplinary, mainly focused upon product development and programme management, in the automotive, aerospace and construction sectors. He is experienced in applying design for manufacture and assembly and lean construction methodologies. His career in the construction sector included being Head of Product and Manufacturing Development, and subsequently Head of Systems and Standards at BAA/Heathrow prior to starting his own consultancy. Part of that has been as an Industry Advisor at Buildoffsite where he leads the Rail Hub. Nigel was the lead author for the BESA/Buildoffsite ‘An Offsite Guide for the Building and Engineering Services Sector’, and the BSI PAS 8820:2016 for specifying low carbon alkali activated cements. He has also authored papers for CIRIA on lean construction, as well as project specifications for Innovate UK and buildingSmart International and contributions to the UK Government’s BIM Strategy.



Our sincere thanks go to all the professionals who have made this guide possible through their contributions. They have generously given their time, providing their expertise and guidance for others who will hopefully be involved in the creation of successful developments above railways, roads or waterways in our cities. Buildoffsite is a collaborative organisation and that is well represented in the manner that this guide has been produced. We thank the organisation for enabling this project to happen and CIRIA’s assistance in publishing it. To all of the contributors for their efforts and willingness to freely share their knowledge, and everyone else who has given permission for material to be included, thank you. Nigel Fraser and Bill Price


About the the contributors About editors Darryl Chen

Graeme Jones

Darryl is a partner at Hawkins\Brown and leads the urban design and research studio, delivering masterplans for brownfield sites, campuses, science parks, housing estates and districts. Darryl has both a client-facing role developing new business and a hands-on design role translating complex briefs into practical design solutions.

Graeme Jones is a specialist in corrosion science and engineering. He is a Fellow of the Institute of Corrosion (FICorr), Level 4 ISO EN15257 cathodic protection designer for reinforced concrete and past Chairman of the E510 Corrosion Committee for the international Concrete Repair Institute (ICRI) in the USA responsible for the drafting and publication of industry guidelines on the evaluation of corrosion and use of mitigation and monitoring systems.

He champions innovation within the practice under the auspices of the &\also thinktank, a research vehicle that informs project briefs, explores new markets and speculates on future directions for architecture and urbanism.

He is Managing Director of C-Probe Group Limited with over 30 years of experience in developing and bringing to market innovative technologies for the low carbon resilience management of structures.

Patrick Hayes

Paul Lambert

Patrick is Head of Structures at Meinhardt UK. He has over thirty years experience in building and infrastructure design. He has a keen interest in industry productivity and offsite construction methods and is a regular speaker and author on the subject.

Paul Lambert is Head of Materials and Corrosion Technology for Mott MacDonald, United Kingdom. He has over 30 years’ experience in structural durability and remediation. Paul is also Visiting Professor at the Centre for Infrastructure Management at Sheffield Hallam University where he researches novel materials, protective coatings and repair technologies.

Ryan Jewell

Steve Lowe

Ryan Jewell is currently Managing Director of Castle Scaffolding Ltd. Utilizing 20+ years of industry experience he has personally overseen the development of the specialist safety netting system - from core inception through to its current day working iteration - designed for use in the Rail Civils Sector.

Steven has over 20 years of bridge and structural design experience in the concept, preliminary and detailed design of a broad variety of bridge types and other large structures in the UK, Ireland and the USA. He has a research Masters from the University of Cambridge, has worked for several top design consultancies, served as a lecturer and is currently the senior design engineer at Shay Murtagh Precast.


Peter McMahon Peter McMahon is an Associate at WSP based in London. He graduated in Engineering from Christ’s College, Cambridge, and is a Chartered Civil and Structural Engineer with eleven years’ experience. His experience of design and construction of significant residential structures includes Keybridge House, Vauxhall, and Queensland Road, Islington. Recently, Peter has been leading WSP’s structural work with Berkeley Modular, developing their new volumetric modular housing solution.

Daniel Richards Daniel Richards is a project manager at MACE Ltd with over 15 years experience of working on major infrastructure projects. In recent years he has specialised in transport hub led development and has overseen mixed use schemes at Walthamstow Station and the overbuild at Twickenham station. He is currently working on a further mixed use development at Guildford Station.

Bernard Williams Nigel Ostime Nigel Ostime is Delivery Director at Hawkins\ Brown Architects, a practice of 275 people based in London, Manchester, Edinburgh and Los Angeles. He leads the recently formed Design Hub at Buildoffsite, which promotes good design and placemaking as well as standardisation and the importance of the DfMA optioneering process during the concept design stage. Placemaking is critical to the successful integration of transport infrastructure into the urban realm.

George Poppe George Poppe is a Chartered Architect and Associate at Sheppard Robson architects, with particular interests in offsite construction and hotel design. His work includes the award winning volumetric modular citizenM hotel above Tower Hill Underground station, within the context of The Tower of London UNESCO World Heritage Site. With his broad knowledge of design for manufacture and assembly products and systems, George is a member of the practice’s Technical Team and gives regular presentations on modular construction.

Bernard is a Chartered Surveyor and practising building economist with a special interest in the economics of offsite construction processes. He is creator and developer of the CombiCycle Comparator web-enabled whole-life cost and sustainability prediction model which has been expanded to incorporate appraisal of offsite construction for comparison with traditional techniques. His expertise embraces the economics of all the stages in the building life-cycle from inception to development and construction and throughout occupation.

Other contributors: Katie Armitt - Lucideon Darren Brookes - Premier Modular Graham Cleland - Berkeley Modular Joe Dyde - Buildoffsite Colin Hibbs - Reform Group Tom Kyle - Sheppard Robson Ali Mafi - Lean Thinking Matt Palmer - Heathrow Airport Jeremy Parker - WSP Luke Murphy - WSP Clare Price - BSI David Whorwood - Ideal Lifts

Peer reviewers: Ivan Dowman - Network Rail Nigel McKay - Buildoffsite John Parker - WSP Karen Shanks - Buildoffsite Anna Winstanley - Lean BIM Strategies Nick Whitehouse - Buildoffsite



Joe Dyde Business Manager, Buildoffsite

Cities like London have an ever-increasing need for additional, good quality housing as they continue to grow. History tells us that targets have been set but are seldom met in terms of creating sufficient residential units. Greenfield sites are often almost non-existent within existing city boundaries, which means that brownfield and demolition sites are the norm for redevelopment projects.

rail overbuild on a scale that has not been achieved in London to date.

In this context, where demolition or remedial costs can be significant, the possibility to embrace innovative infrastructure overbuild approaches becomes an exciting new alternative - one which becomes even more attractive where the infrastructure corridor land is in quasi-public ownership.

I would like to thank all those who have contributed to the production of this guide, and hope that it will help site owners and potential developers unlock the potential of such projects in the near future.

Such sites can improve and link up surrounding neighbourhoods and revitalise areas. This has been demonstrated in a similar context north of Kings Cross and St Pancras Stations in London. In these locations, former goods yards, gas works and market areas have been cleared (above a myriad of tunnels) to reconnect the boroughs of Camden and Islington. This has attracted numerous high value commercial and educational organisations, as well as residential development. Over the last two decades, significant overbuild has taken place internationally, most notably in New York and Paris. WSP has published two ‘Out of Thin Air’ reports that clearly illustrate the potential for

The challenge is to make such sites economically viable. The safe creation of supporting structures in the form of a deck or raft is key to this. In this guide we have set out to demonstrate how using offsite solutions can contribute to this form of development.

Contents About the editors




About the contributors Preface

06 08



Chapters: 01

Place making opportunities Darryl Chen, Hawkins\Brown



Engineering the deck Peter McMahon, WSP



Development on the deck George Poppe, Sheppard Robson



The economics


Bernard Williams, IFPI 05

Potential future innovations Nigel Fraser, Buildoffsite





Nigel Fraser, Buildoffsite 07

Global initiatives and expertise


Bill Price, WSP 08



Patrick Hayes, Meinhardt 09

Risk management Patrick Hayes, Meinhardt



Project management and case study


Daniel Richards, MACE Conclusions





Introduction Background and Aims In November 2018 WSP published the ‘Out of Thin Air – Building over London’s rail lines’ report, which identified the potential for creating overbuild sites for as many as 250,000 residential units (100m2 per unit) in London. The supporting analysis was rigorous and based upon several general assumptions. Subsequently WSP refined this, publishing “Out of Thin Air – One year on” in 2019. In this report further criteria were applied to home in on the most likely sites for development. Following the publication of the first report, the Buildoffsite Rail Hub decided to look at how offsite methods could be used to maximise this opportunity, with the objective of making such projects more interesting to a wider range of developers and offsite construction specialists. The result is this collaborative piece of work with contributions from numerous Buildoffsite members, with different industry leaders providing each chapter. The current housing shortage along with the objective of investing in infrastructure has resulted in oversite development being examined by transport bodies as a solution to both issues. Transport for London (TfL) have been mandated by the mayor to deliver social housing. Their business plan1 sets a target of building 10,000 homes in London by 2020/21. Network Rail have similarly been asked to support the Government’s Housing Target by releasing public land2 . However, these targets are modest compared to the scale of opportunities indicated by the WSP reports and tend to include easier development opportunities relating to sites such as depots rather than building over the main lines. The scale of overbuild to date has also been modest in London when compared to that in other cities, such as Paris, where extensive overbuild has taken place over both railway lines and major roads. In the creation of this guide, a number of workshops, meetings and one-to-one discussions have taken place. During these, numerous examples of overbuild projects have been identified, both in the UK and abroad. Many of these demonstrated risks and opportunities that need to be managed. Such projects have highlighted how the specifics of working adjacent to operational railways has resulted in unexpected complexity and costs, leading to challenging commercial outcomes. An interviewee quoted in the Hansford Review3 opined that projects would need to be worth at least £200m to justify the complexities. This guide aims to help industry practitioners understand the challenges of overbuild projects and plan them more effectively, with more confidence in the outcomes, hopefully bringing the viable size of projects down. The recent redevelopment of Twickenham Station has demonstrated that smaller projects can be viable and that has mainly used offsite methods for the support structure and facades. More can be done in this respect and this guide aims to help achieve this.

1. Transport for London Business Plan 2019/20 to 2023/24, Transport for London, December 2018 2. Development: Open for Business, Network Rail Property, Sept 2017 3. The Hansford Review Unlocking rail investment – building confidence, reducing costs, Peter Hansford Freng, June 2017 4. Out of Thin Air: Building Above London’s Rail Lines, WSP, November 2017 5. Out of Thin Air: One Year On, WSP, November 2018.


The Role of Offsite

A Fundamental principle of oversite development (OSD) is to design to minimise construction risk by reducing the interfaces between the rail system and OSD, both physically and in time. Overbuild sites will inevitably be complex and relatively expensive to develop. However, the tipping point between viability or not may be moved in a site’s favour through a range of actions such as: • • • • • • •

Efficient construction of the enclosure/support box Utilising lower mass super-structures to reduce foundation and support structure costs Reducing the number of activities that would require a “possession” of the operational infrastructure below Accelerating the build using offsite systems to reduce time-related costs and risks Providing greater time and cost certainty Achieving high sustainability performance in use De-risking the project for developers, contractors and infrastructure owners

As the recent redevelopment of New Street Station in Birmingham demonstrated, the experience and capabilities of the mechanical and electrical services provider, Bailey Offsite, brought a novel approach to working over operational platforms and railway lines. Offsite solutions can change the way things are done. Prefabrication takes work away from the site. This is particularly attractive where a facility needs to remain operational. The less construction the traveller is exposed to the more normal their journey will seem. It does, however, require a different approach to the initial design and planning applications, scheduling work, logistics and cash flow management. There are strong reasons for deploying an offsite based approach to overbuild projects. This needs to be recognised at the outset of the project, before planning approvals, to get the full benefits. This guide should help navigate the journey.






Lines of opportunity The great era of railway building that commenced with the commercialisation of steam power brought about profound changes in the geographies of towns, cities and regions across the country. Railways were a revolution in connectivity, unburdening whole populations from finding economic ties in local areas. Metropolitan rail facilitated sustained growth of British cities throughout the Victorian era, culminating in the early twentieth century commuter suburbs of Metroland. What brought growth, mobility and prosperity to millions also had profound consequences for the physical places where railways were situated. The railways displaced development on land that might otherwise have been more directly economically productive. Furthermore, the presence of new railways blighted adjacent and nearby properties with environmental nuisance. Even rail electrification failed to eliminate the negative aspects of the railways as a source of noise, dust and vibration. Many an urban area bears the scars of a formerly connected neighbourhood riven by railways. Often maps reveal streets aligned on both sides of a railway where there used to be continuous urban fabric. The means now exists to bring railway corridors back into productive use. Rail overbuild projects have the potential not only to reclaim new development land, but also improve the quality of neighbourhoods, towns and cities. In fact, the greatest consequence of restoring railways as new development land will be the effect on place-making beyond their site boundaries. A number of studies have been undertaken in the period 2016 – 2019 for rebuilding Clapham Junction railway station in London. Within this chapter are several images to illustrate how the station and wider area could be regenerated whilst providing a very large number of new homes. Figure 1.1 shows a vision of place-making over the multi-track station interchange.

Optimal development sites The physical space that railways occupy represents a large quantity of land that can be developed under the right circumstances. Pressures on many cities to provide housing, employment and amenities means that public and private sector developers alike are securing new development land and ensuring that subsequent development makes the most of its potential. In London, a central tenet of the Mayor’s Good Growth agenda is to optimise the use of land. That is, to build sustainable densities and incorporate a vibrant mix of uses. Beyond London, this directive is echoed in urban areas around the country. Rail corridors, including the track space and adjacent operational land, consistently provide the right dimensions of space necessary to bring forward residential and employment uses at scale. Here is an opportunity to realise a significant amount of new development to help tackle a city’s growing needs.

Revalued neighbours Rail corridors themselves are sources of environmental nuisance. They affect the quality of life for those who live beside them, in terms of decreasing the quality of air and increasing disruption through noise and vibration. The poorer environment diminishes the value of those properties around railways, in many cases restricting land to industrial uses. Developing over rail tracks will have the benefit of containing noise and pollution so that they no longer provide negative effects to those who live beside them. Tunnelising or culverting trains as the primary source of nuisance will set the platform for a good neighbour to surrounding properties, which should have the benefit of increasing value. Figure 1.2 shows how a deck over the new station could lead to enhanced connectivity.

Lead Author Darryl Chen, Hawkins \ Brown


Figure 1.1 Potential regeneration at Clapham Junction, London. Image ŠHawkins\Brown & Mott MacDonald


Figure 1.2 Connectivity and place-making links around Clapham Junction Image ŠHawkins\Brown & Mott MacDonald


Connected communities New over-track development should be seen as a restorative urban operation that repairs a source of severance. Increased connectivity can provide new means for more people to access community assets and places of employment that lie on either side of railways. Increased accessibility and legibility by sustainable modes of transport should allow greater economic opportunity to town centres as footfall increases. Social value will increase commensurate with economic value. Where connections across the rail corridor can be made, over-track development should relieve traffic congestion by creating new crossings and distributing driving routes throughout a more extensive grid. An urban structure with more networks will effectively remove pinch points. The vast majority of town centres are situated around rail stations, and therefore stand to gain significantly through over-track development. Bringing rail land into developments will enhance town centres and allow them to grow in the economic, social and environmental aspects that mark sustainable growth, creating additional retail and employment capacity, increasing footfall and improving environmental qualities. Overtrack development will create connected neighbourhoods and better town centres. Figure 1.3 shows how level changes could be overcome in support of a mix of commercial uses alongside new homes.

Figure 1.3 A town centre approach to addressing level changes to accommodate the station beneath Image ŠHawkins\Brown & Mott MacDonald



Figure 1.4 A masterplan vision for Clapham Junction providing homes alongside commercial and community uses together with a 21st century station interchange Image ŠHawkins\Brown & Mott MacDonald

Development risks The linear nature of railways means that any development opportunity will take on a distinctive urban form. It is interesting that the shape of over-track development sites ensures that they cannot be enclaves. By nature they interface with a maximum number of properties and stakeholders. Development will necessarily proceed with a high level of participation from neighbours in order to ensure that benefits are extended to as wide a number of people as possible. Neglecting stakeholder engagement risks missing the main place-making driver for development in the first place. Clearly developing over railways will involve enabling infrastructure whose costs represent an additional burden as compared with normal site development appraisals. Financial viability may well upwardly drive development quantum, thereby raising the risk of over-development in terms of townscape, local character and amenity to existing communities. Furthermore, the revaluation of land in the vicinity of over-track development may mean that industrial land uses are displaced through upward pressure on land value. Development must proceed in a way that preserves places of employment and uses that provide vital ‘urban services’ to metropolitan populations. These threats underline the necessity for a masterplan approach that has place-making at its heart. In Figure 1.4 is a vision for how a major regeneration could occur above and around a major new masterplan for Clapham Junction.


Engineering the deck

2 1

Rail encapsulation The provision of a structural deck is the cornerstone of an overbuild development, providing a horizontal platform for development of the site. Additionally, in forming walls and a deck around the railway, the railway is encapsulated safely, providing a barrier and boundary between the realms of the railway and the development. It is recommended that the deck be constructed in reinforced concrete to address fire, robustness, and maintenance issues. It should make use of offsite manufactured members, and make the most of opportunities such as low carbon concrete, lightweight concrete, and self-compacting concrete. Vibration control should be addressed outside of the box, within the realm of the development rather than the railway. Figure 2.1 illustrates the principle of rail encapsulation.

Lead Author Peter McMahon, WSP Figure 2.1 Rail encapsulation with overbuild development Image ŠWSP


Figure 2.2 Structural form: typical span and height

Structural form Indicative overbuild spans and heights are illustrated in Figure 2.2 above. There are many different configurations of rail tracks. In some cases, the configuration and spacing of tracks has evolved over many years as the rail corridor has expanded or reduced. Studies carried out by WSP and Network Rail have examined different spans and heights of encapsulation arrangements. Any given site should be assessed on its specific conditions in terms of physical geometry as well as rail operations. In some cases, this can lead to the walls being within the track-side “impact zone”.

Minimum height of the box above the rail In most cases a minimum height of 5.8m is adequate, based on train speeds up to 100mph, and based on overhead line equipment being fixed to the box structure. In some situations, a height of 5.4m may be acceptable. Consultation with Network Rail asset protection engineers is advisable.

Minimise the width of the box It is recommended that the box be made as compact as possible, placing walls within the “rail impact zone”, where Eurocode 1 requires their design to resist an impact load. This approach reduces structural spans and maximises development space. An oversite development load corresponding to approximately 10 storeys of modular frame is the tipping point at which the wall and foundation design is governed by vertical forces rather than by the horizontal impact load. The presence of track-side signals, cables and other Rail Systems equipment may, however, dictate that a longer span is more economical. It is sometimes very expensive to move such equipment, and signal sighting issues can require a greater lateral clearance.

Figure 2.3 Structural form: typical structural elements


Deck Precast, prestressed bridge beams are recommended to suit rapid assembly within the constraints of track closures. They can efficiently span the track arrangements shown in Figure 2.2, and can be combined with in-situ infill and topping concrete. Attention should be paid to deflection limits specified by the manufacturer of modular overbuild components. Beams placed close together, with in-situ concrete infill, are likely to be the optimal solution. Precast “MY” beams are likely to be appropriate for shorter spans, and “TY” beams for longer or more heavily loaded spans. For the longest and most heavily loaded spans, deeper downstand beams placed at wider centres, with in-situ concrete topping slabs, are likely to be the preferred approach. The beams should be positioned directly below concentrated loads. Reducing and distributing loading on the deck as far as possible is preferable and will minimise the size and cost of the deck, walls and foundations. Loading can be reduced by favourable massing of buildings on the site, adopting lightweight modular systems and by specifying lightweight concrete. Figures 2.4 and 2.5 show indicative deck depths and sections for 11m and 23m spans, for a deck with “TY” beams providing a flat soffit. Indicative depths have been calculated on the basis that precast beam and wall units would be concreted together on site to provide a continuous structure. Figure 2.6 shows precast beams with an in-situ topping being installed at Twickenham Station, London in 2018.

Figure 2.4 Precast, prestressed deck: typical deck depths Chart ©WSP & Shay Murtagh

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Figure 2.5 Precast, prestressed deck: typical deck sections Diagram ©WSP & Shay Murtagh


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Figure 2.5 Typical section precast MY, TY, and W beam decks

Figure 2.6 Precast deck installation at Twickenham station, London. Courtesy of Banagher Precast Concrete. Images ŠBanagher Precast Concrete


Walls Solid continuous concrete walls are preferred to individual columns, providing total enclosure to better contain rail impact events and provide improved acoustic isolation. Openings required for ventilation and access are site specific and addressable as part of the design and approval process. It is advisable to keep these over 1.8m above track level, with the structure below this point resisting derailment loads. Fire protection can likewise be addressed as part of the design and approval process.

Precast concrete wall panels These offer programme and safety advantages, simplifying the construction process. Where multiple deck spans are used, typical wall thicknesses of 800mm are recommended, widening at the top to 1400mm to provide bearing for beams. For single span decks, 1200mm thick walls are recommended.

Twinwall These consist of a pair of precast concrete permanent shutters with reinforcement and in-situ concrete. They offer improvements in robustness and ability to resist derailment impact loads. They also offer flexibility in adapting to different loads and requirements for openings. It would also be possible to provide twinwall panels between precast concrete columns or encased steel columns. Self-compacting concrete is recommended to improve safety and eliminate the need to vibrate concrete during the pour.

Figure 2.1 Rail encapsulation and deck with overbuild development (image courtesy of WSP)

Structural form There are many different configurations of rail tracks. In some cases, the configurations and track spacing has evolved over many years as the rail corridor has expanded or reduced. Studies carried out by WSP and Network Rail have examined different span and height of encapsulation arrangements. It remains the case, however, that a given site should be assessed on specific conditions in terms of physical geometry as well as rail operations. Figure 2.2 shows some typical scenarios where the walls are within the impact zone.

Rail encapsulation

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There are many different configurations of rail tracks. In some cases, the configurations and track spacing has evolved over many years as the rail corridor has expanded or reduced. Studies carried out by WSP and Network Rail have examined different span and height of encapsulation arrangements. It remains the case, however, that a given site should be assessed on specific conditions in terms of physical geometry as well as rail operations. Figure 2.2 shows some typical scenarios where the walls are within the impact zone.

Figure 2.7 Precast wall sections installed at Twickenham Station, London1. Courtesy of Banagher Precast Concrete, Image ŠBanagher Precast Concrete 1 Project: Twickenham Station Overbuild; Client: Solum/Network Rail; Consultant Engineer: Watermans; Contractor: Oliver Connell & Sons; Precast Supplier: Banagher Precast Concrete


Foundations and enabling works Piled foundations are likely to be required, with a variety of possibilities depending on the site. Depending on loading and site conditions piles, can be arranged as a single row or in pairs if adequate space is available. Pile caps and any shallow foundations should be shallow enough to remain above a 45˚ line from the underside of the sleeper, in order to reduce the need for propping to excavations as illustrated in Figure 2.8. The preferable situation is a site with level access, and a low headroom piling rig with a low centre of gravity to reduce the risk of overturning. Preferably there should be space to operate the rig perpendicular to the track and segregated from it, without the need for the track possessions. Track possessions are likely to be required for both geotechnical investigation and for surveys of railway infrastructure. Specialist input is required to determine what work is necessary to move, divert or replace railway infrastructure, and to navigate the project through the relevant approvals processes.

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Lateral stability

The approach taken to resisting horizontal loads will vary significantly depending on the scheme context. Some horizontal forces may be resisted by the box itself, along its walls as well as across the box in traditional ‘frame action’. Preferably, horizontal forces should be resisted by separate core structures positioned to the side of the overbuild box and railway. In some locations this could enable access to overbuild property at ground level. Where horizontal forces are to be transferred through the overbuild box itself, the implications for the deck should be considered at an early stage. Heavy concrete cores positioned over the deck should be avoided. Braced steel alternatives could be considered, as could modular framing with load bearing walls.


Case study: Royal Mint Gardens, London An overbuild box was constructed around the Docklands Light Railway near Tower Hill and is shown in Figures 2.9 and 2.10. The site provided good access to both sides of the railway. Foundations were piled, with a mixture of separate piles and contiguous and secant pile walls to suit basement development adjacent to the railway. These were installed without track possessions. Walls were formed of separate precast sections, installed using an excavator without over sailing the railway. The deck was formed from precast concrete beams with an in-situ topping, and was installed over a single 72-hour track possession. In this case a very light deck was provided and the overbuild includes separate transfer structures, as can be seen in Figure 2.11.


These consist of a pair of precast concrete permanent shutters with reinforcement and in situ concrete. They offer improvements in robustness and ability to resist derailment impact loads. They also offer flexibility in adapting to different loads and requirements for openings. It would also be possible to provide twinwall panels between precast concrete columns or encased steel columns. Self-compacting concrete is recommended to reduce the safety and programme requirements of vibrating concrete on site.

Rail encapsulation

Provision of a structural deck is the cornerstone of an overbuild development, providing a horizontal platform for development of the site. Additionally, in forming columns, walls and a deck around the railway, there is an opportunity to encapsulate the railway safely, providing a barrier and boundary between the realms of the railway and the development. It is recommended that the deck be constructed in reinforced concrete to help address fire, robustness and maintenance issues. It should make use of offsite manufactured members, and make the most of opportunities such as low carbon concrete, lightweight concrete and selfcompacting concrete. Vibration control should be addressed outside of the box, within the realm of the development rather than the railway. Figure 2.1 illustrates the principle of rail encapsulation.


Figure 2.9 Installation of overbuild box walls at Royal Mint Gardens. Courtesy of Jeremy Parker. Image ©WSP Figure 2.1 Rail encapsulation and deck with overbuild development (image courtesy of WSP)

Structural form There are many different configurations of rail tracks. In some cases, the configurations and track spacing has evolved over many years as the rail corridor has expanded or reduced. Studies carried out by WSP and Network Rail have examined different span and height of encapsulation Figure 2.5 Precast wall sections installed at Twickenham Station, London. Courtesyon ofspecific Banagher Precast Concrete. arrangements. It remains the case, however, that a given site should be assessed conditions in terms of physical geometry as well as rail operations. Figure 2.2 shows some typical scenarios where the walls are within the impact zone.

Foundations and enabling works Rail encapsulation

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Figure 2.10 Installation of overbuild beams at Royal Mint Gardens1. Courtesy of Banagher Precast Concrete. Image ©Banagher Precast Concrete

1 Project: Royal Mint Gardens, DLR Encapsulation; Client: IJM Land/ DLR (Network Rail); Consultant engineer: WSP; Contractor: Carey’s; Precast Supplier: Banagher Precast Concrete


Figure 2.11 Overbuild at Royal Mint Gardens. Courtesy of Jeremy Parker. Image ©WSP

Summary The preferred deck solution encapsulates the railway in a concrete box and segregates the realms of the railway and the development from an early stage. This box is likely to be most efficient if minimised in span, even if design to resist rail impact loads will then be required. Offsite manufacture of precast elements is preferred to suit rapid construction of the walls and the deck. Piled foundations are likely to be required. Specialist input will be required to design and obtain approval of work required to railway infrastructure.

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The key structural components of the rail encapsulation approach are described in Table 2.1.

The box

Consider use of low carbon, lightweight, self-compacting concrete if appropriate.


Vibration Isolation Wall openings for ventilation and access.

Creation of a ‘tunnel’.

Overbuild loads minimised using lightweight modular.

Structural form

Spans up to 23m. Flat soffit - precast beams with in-situ infill and/or topping.


Longer spans.

Overly complex stability systems.

In-situ concrete.

Metal deck materials requiring extensive maintenance.

Deep downstand beams to suit concentrated loading.

Steel trussing.

Precast walls.

Precast columns.



In-situ concrete.

Steel framing requiring maintenance.


Piled foundations.


Complexity leading to delay.

Separate core positioned offdeck.

Horizontal loads resisted by box structure.

Horizontal loads distributed to deck through modular walls.

Steel core structure positioned above deck.

Lateral stability

Table 2.1: Key structural components of the rail encapsulation approach

Reinforced concrete (heavy) core structure positioned above deck.


Development on the deck


Site conditions, constraints and opportunities Development over railway lines within urban areas will need to address a variety of conditions: differing track levels (at grade, elevated, within a cutting); a variety of edge conditions; daylight, sunlight, and rights to light restrictions; and varying degrees of street connectivity. Our challenge in attempting to provide guidance for the architectural response to such a wide range of possibilities was to find the commonalities and unique opportunities that the various conditions provide. Our concepts have been developed based upon a theoretical series of sites which comprise typical conditions identified across many kilometres of railway lines throughout the UK, and take into account previous successful rail overbuild developments. The scale of rail overbuild developments will need to be tailored to their urban contexts. Here we have illustrated two principle building models: low scale terrace houses or stacked maisonettes, and taller multi-storey apartment buildings. These are both successful typologies which provide high-quality homes in accordance with current best practice guidance, and can be adapted to address the numerous site orientations, configurations and contextual conditions. Over-Station Developments (OSDs), which build over stations or transport hubs sites, generally have the potential to achieve greater height and scale than at sites between stations. An increased building density is required to make complicated OSD schemes viable, and precedents include Twickenham, Paddington, Fulham Broadway, Southwark, Farringdon and Euston stations.

Access and servicing Issues of access and servicing are common to most railway sites suitable for overbuild development, many of which are characterised by sensitive edge conditions—such as borders with domestic gardens that are sensitive to overshadowing and overlooking, or the stark facades of industrial units. The boundary conditions do not always provide an attractive aspect for high-quality new developments. Our architectural response to this unlocks the development potential of such sites by using the new platform over the railway as a street. This street does not need to have vehicular traffic. It may need to be narrower than a suburban road—due to the width of the rail land—and could be better conceived as a strip park that incorporates pedestrian walkways and cycle routes. This concept generates an appropriate focus and outlook for the residential buildings, whilst providing a new transport network or leisure promenade at the heart of the scheme to facilitate the connection of previously divided neighbourhoods. The buildings on either side will frame the central route, and thus cores will most sensibly be located to each side of the railway lines, helping to reduce load transfer and in certain conditions allowing direct access to the lifts from ground floor level where the railway is at grade. A plan illustrating this approach is shown in Figure 3.3 and the corresponding section in Et parisciis aut3.4. faccusa Figure

Lead Author George Poppe, Sheppard Robson


Figure 3.1 Typical railway condition 1: within a cutting

Figure 3.2 Typical railway condition 2: at grade


Figure 3.3 Low scale stacked homes over the rail corridor

Figure 3.4 Typical floor layout for taller apartment building over the rail corridor


Offsite construction For the development atop ‘the box’, as outlined in Chapter 2, various offsite methodologies could be employed to form the superstructure of the buildings, including: • • • • •

Four-sided modules Partially open-sided and open-ended modules Open-sided (corner supported) modules Mixed modules and planar floor cassettes Modules supported by a primary structural frame

Other module types: • • •

Stair or lift modules Non-load bearing “pods” Open floor modules

For the conceptual approach illustrated, we advocate for the use of volumetric modular construction. This methodology offers the potential to bring to site the most complete prefabricated building components, including some MEP services, and presents significant advantages for developments of this nature. Currently, volumetric developments in the UK can achieve heights of up to around 45-storeys. The building typologies we have developed are based on volumetric modular components, sized according to best practice industry standards and UK transport regulations. In addition to the ‘standard’ benefits that volumetric construction offers – whereby many operations can be completed off-site, such as assembly of components (including glazing and cladding), benchmarking and prototyping, testing (acoustic, thermal, MEP (partial), weather, stacking), quality control and defect rectification, first fix services installation, finishes and furniture fit-out, and Building Control Approval (partial) – the following attributes make volumetric construction a particularly appropriate solution for rail overbuild developments: • • • •

• • • •

Reduced weight of construction when compared with traditional techniques This helps to reduce the structural depth of ‘the box’, and because modules are self-supporting structural components, no separate superstructure is required Enhanced acoustic performance and vibration isolation Vibration from the railway can be mitigated through the installation of isolation bearings between ‘the box’ and the lowest module. Structural separation between the modules prevents vibrations from spreading vertically throughout the building, and acoustic floors and ceilings provide attenuation for both airborne and impact noise Shorter on-site construction programme The substructure and modules are built concurrently rather than sequentially. The shorter construction programme reduces noise and disruption for the local community. Developments can be brought to market more quickly; Fewer, larger, components lifted by crane A good solution for awkward or constrained sites, disruption to the railway and the number of track possessions required are reduced. The number of tradespersons on-site is less than traditional sites and associated safer working methods and conditions provide CDM benefits

Other considerations associated with volumetric modular construction that should be reviewed include: • • • • •

Access from factory to site and transport logistics considerations Complete design sign-off to enable modular manufacture to begin Opportunities to change the design later on are significantly reduced, so client confidence is key Cash flow is different to traditional construction and procurement Thicker internal walls and taller floor-to-floor heights need to be factored into the design due to double wall/floor/ceiling construction at module-module and module-core interfaces

Appropriate building typologies It is presumed that most rail overbuild developments will be residential-led due to continued need for housing in UK cities. Offsite construction techniques can deliver all forms of residential accommodation, including private sale, affordable, build-to-rent, student accommodation, co-living, hostels and hotels. The ground floor could provide a mixture of day and evening amenities. These would add vibrancy to the development and contribute positively to the wider community with offices, retail units, bars, restaurants, cafes, healthcare services, education facilities and other community uses.


Et parisciis aut faccusa Figure 3.5 Concept sketch of new ‘streets’ created over railway lines


Figures 3.5 & 3.6 Illustrative view within the street above the railway


Economic considerations

Land for development

4 1

Building over linear infrastructure, particularly above railways, usually releases brownfield sites of the best order in terms of communications and amenity. Many are suitable for mixed residential and commercial development. They are also owned by authorities that have limited interest in property development as a mainstream business, so have the potential to be released as required, provided this does not impinge upon the efficiency of the operating service. Historically infrastructure overbuilding has generally been carried out in UK without creating undue problems of operational efficiency for the rail or roadway. However, the costs of risk avoidance on low density schemes can sometimes severely discount the value of land, which might otherwise be released.

The value of land for development Land has very little value unless it can be developed. The developed value comes from a residual calculation that is quite simply: LV = DV – (C + P) where LV = land value; DV = value of completed development, C = total costs of development (excluding land) and P = development profit. In the case of rail overbuilding, the residual land value from this equation is further reduced by the cost of the podium and enabling works. So the equation reads: LV = (DV – (C + P)) – EW where EW = Enabling Works including podium (decking/encapsulation) It should, however, be noted that a significant part of the podium cost would otherwise be incurred in oversite construction on a conventional site in terms of foundations. Finance can play a significant part in determining the overall cost of development, especially where the land is sold to the developer at the outset and incurs charges on the full amount until the development matures. However, in infrastructure overbuilding it is common for the landowner and developer to go into a JV, which avoids the cost of finance on the land and makes the project marginally - or sometimes significantly - more viable. When calculating the residual value of development land, the valuers usually price the construction work at current rates for works built in traditional or modern conventional processes and allow a normal contract period when calculating the finance costs for the development. It is unusual for developers’ valuers to price offsite construction methods at less than traditional costs. If they do consider using modern methods of construction (MMC), it will normally be for the purposes of bringing forward profits and/or sales in a bull market through speed of construction. Putting all this theory into real numbers, a site of 1.0 Ha with planning permission for a mixed development of say 40,000 m2 gross internal area (GIA) might have a residual land value of £20m after allowing for the costs of the podium, temporary works, landlord’s operational costs and enabling works.

Lead Author Bernard Williams, IFPI


On the other hand, if the permitted development only amounted to say 20,000 m2 GIA with a largish proportion of affordable housing, the residual land value might only be around £5m. With podium and enabling works costing say £10m, the risk/reward of such a development would not be at all attractive to the landowner. Both of these examples are shown in the chart below.

Figure 4.1 Two illustrative scenarios Where overbuild sites have good intrinsic development value with permission for an adequate volume of valuable property development, the discounting effect of the podium and enabling work should not be a deterrent to release of land. The major factor then in determining the economic viability of rail overbuilding is the volume and nature of development for which planning permission is granted. The cost of the podium and enabling works is therefore most significant if there is inadequate density of development.

The impact of construction cost and speed on development viability MMC offers significant speed of construction advantages. The costs of offsite construction processes in the UK in recent times have also come a lot closer to conventional onsite methods. In some cases builder and developers are making savings through use of MMC. But this can be a double-edged sword. For example, in housebuilding where the vagaries of supply and demand on speed of sales can sometimes negate the speed-related benefits of offsite construction. Time-related savings in site preliminaries, lower waste of materials and lower development finance can offset all or part of any additional construction costs. However, sometimes developers select offsite processes inappropriately – especially when introducing structural frames where cellular layouts would otherwise permit the adoption of load-bearing masonry walls – leaving the impression that offsite solutions can be more expensive. That being said, in practical terms the cost of construction pales into insignificance the greater the value of the completed development. With luxury residential accommodation and high value commercial uses, the effects of higher construction costs have only a small impact on development profitability. Consequently, developers are only likely to opt for MMC – even at a cost premium – in order to bring forward the profit-taking or to take advantage of favourable market conditions. Of course, acceleration of the traditional process can often bring about the same result but here the extra cost is inevitable, whereas it may not be incurred in MMC. There are further benefits too. It has been demonstrated that offsite approaches can deliver significant capital cost savings as well as other business and operational benefits in the infrastructure sector, in particular where a standard product-based approach can be deployed. Serial clients have exploited this, including in the transport sector where the impacts on passengers have needed to be minimised. Buildoffsite case studies are available for a range of projects.


Other benefits of MMC Other factors that may influence developers to adopt MMC include: • • •

Better quality control Improved air-tightness Price and time certainty

On the other hand, there may well be a loss of flexibility in changing layouts and specifications to meet unforeseen circumstances. Most of these issues apply equally to infrastructure overbuilding as to conventional site development. So, it is really only in the podium where the speed of construction available from MMC can have an exceptional advantage. Furthermore, these benefits will accrue mainly to the operator/landowner, rather than to the commercial developer.

MMC and the podium works Where the cost of the podium is only a small amount relative to the land value, the main advantage of adopting offsite construction is in minimising the disruption to the basic operation. Any cost premiums will be swallowed up in the high residual land value. The risk reduction and lower down-time in respect of the basic operations will of course be welcome and generate an additional incentive to land release. However, where the project land value is marginal, even where the cost of the podium can be reduced, it is unlikely that the landowner will want to take the risk of the cost reduction not being achieved if such failure would make the residual land value fall to unacceptable levels. The following graph illustrates the variability of encapsulation costs for a selection of overbuild sites that are not linked to station redevelopment. The construction cost includes foundations, walls and decking suitable for modular overbuild of 12 storeys. It also includes contractor allowances for overheads, preliminaries and profit and an estimate of rail possessions to carry out the work.

Et parisciis aut faccusa

Figure 4.2 Comparison of a range of encapsulation development costs, excluding rail enabling works Image ©WSP


Historically the focus has been on capital cost rather than whole-life cost optimisation. Where a landowner has a long term interest in assuring the condition of a structure above their transport system, there are opportunities to minimise whole life maintenance costs by incorporating active structural healthcare systems from day one. Incorporating such systems with the initial build is significantly lower cost than retrofitting them 15 years later. The incorporation of a monitoring system from day one may add 0.1-0.3% to the capital cost. The inclusion of a corrosion control system may add 5%. However, if added at the time of the first repair contract, this could add up to 25% to the repair contract, according to C-Probe Systems. Without such protection, significant repairs may be needed at 25-year intervals, for example. Further information on this is provided in chapter 5.

Should MMC be more expensive than traditional construction? As discussed briefly above, MMC costs in the UK are becoming more competitive. Where costs are higher than traditional, it is because either: • • •

Suppliers need to amortise their investment costs over a short period of time; Solutions are inappropriate to the circumstances; Initial designers have not been well informed with respect to cost drivers for MMC

Outside the UK, there are many examples of offsite construction proving significantly cheaper than traditional though. Research carried out on behalf of the EU in recent times has shown that many countries that major on MMC are building at some 20% to 30% less than the UK for comparable construction types. Current research in the USA bears this out for low-medium rise residential development in timber frame, for example. The UK government has clearly put its support behind MMC with a view to improving the UK construction sector’s productivity. This is manifest in the launch of the Core Innovation Hub in 2019 and the wider Industry Strategy. One focus on developing modular, system-based platforms that are configurable for multiple projects and interoperable standards should see costs being driven down. This has already started in the civil engineering world with well-developed design guides for precast structural systems. Recent developments for systematised design in the application of London’s residential unit design standards could be used for the superstructure. As suppliers are able to reduce prices through such developments, MMC solutions are likely to be more widely adopted and understood. Other factors, such as reduced impact on infrastructure operations and passengers, speed, quality and price certainty, will always attract some UK developers – and infrastructure landowners - to the MMC proposition and its role to play in overbuild.


Potential future innovations Predicting the future is a risky business, particularly in a sector as conservative as construction. But it is clear that we need to advance in this domain or overbuild sites will be considered too risky, too expensive to develop, or both.

5 1

This chapter therefore focuses upon several emerging technologies and approaches that are being accepted in other areas of construction and restoration of the built environment. Innovations that already have some provenance. Here we consider: •

Demand side Ȉ People’s evolving needs and increasing population density Ȉ Uses of space within the structure Supply side Ȉ Reducing the carbon footprint, including embedded carbon Ȉ Reducing fire risk Ȉ Designing for indefinite life Ȉ The Internet of Things Ȉ New standards for modularization Ȉ 3D scanning and the positional accuracy of construction assembly Ȉ Digital based processes - BIM and the automation of design and construction Ȉ New manufacturing processes Ȉ New assembly processes Ȉ Stakeholder approvals Ȉ The reducing elapse time (and related costs, including railway possessions) Ȉ The use of consolidation/logistics centres Ȉ Horizontal packaging of mechanical and electrical services Ȉ Reducing weight of components

Lead Author Nigel Fraser, Buildoffsite


People’s evolving needs and increasing population density Innovation should respond to society’s needs. We are seeing the sharing society develop and technological trends reducing the space we use. Some of the homes of the future could be quite different to those of the present.

Different ways of living Concentrations of people and facilities around transport hubs where people can socialise easily, shop frequently, pop to a nearby gym, have access to a range of transport options and lounge and relaxation areas may require less of their own living space. Home House, a luxury club in Marylebone, or the Executive Floor lounges one finds in hotels may be exclusive but could provide a model for new ways of living. Young people saving hard to buy their own home may prefer smaller units. “Studette apartments” (or small studio apartments) in Paris are very small (12+m2) and less functional than the smallest units envisaged in current plans for London, but they may become part of the mix if the wider environment provides adequate facilities. This could increase the density of an overbuild development without necessarily compromising quality of life. This represents an extension of a society with greater emphasis on sharing facilities. This does not, however, fit with the current planning guidelines for London.

Figure 5.1 The layout of offsite produced MoD single person accommodation wing that incorporates shared facilities Image ©Premier Modular.


Permitted heights of developments In “Tall Buildings A Strategic Design Guide” (edited by Clark and Price) the section by Nigel Bidwell on Urban Regeneration discusses the importance of the public realm, citing examples of podiums on which tall buildings sit. To be commercially vibrant and interesting, these need a concentration of people who will use the facilities on or in a podium. Height helps enable greater population density, along with the point made above. Height - specifically the number of floors - helps create commercial scale and improve the viability of a development.

Figure 5.2 Taller scale developments at transport hubs Image ©Sheppard Robson Architects

Et parisciis aut faccusa


The changing needs of residential occupiers Social housing, in particular, can have changing needs with regards to how residential units are divided up. This is also true of how families want to use properties when young adults leave home. There is a case for considering reconfigurable, non-structural walling systems. Buildoffsite member, Reform Group has developed one such system, which started life in the museums and galleries sector and more recently in retail, healthcare and commercial settings, where there is a need to be able to erect, move and delete walls using reconfigurable, reusable systems and sustainable methods.

Use of space within the structure In overbuild schemes, structural spans can be very large and, as a result, the supporting structural frame can be very deep. Typically this space would be unexploited. However, provided the containment performance required of the rail or road system operating beneath it can be assured, there are a range of uses which space with little or no access to daylight are suitable for. As long as other functional requirements can be met, for example fire, acoustic, ventilation etc. Uses such as casinos, shops, vehicle parking and even hotels (see Yotel) may be able to use such space. The structural members may provide support to such floors from their base, whilst providing their primary role of holding up that, which is built upon them. The bridging structure may even be in the form of trusses, where the lower level is supporting the upper frame, for example above railway platforms.

Figure 5.3 BAA Pier Strategy - arrivals corridor hangers are vertical truss members supporting the roof Image ŠHeathrow Airport


Demand side summary These three changes have implications for both the overbuild concept and the types of offsite units that they would be composed of, as well as highlighting the need for flexibility in reconfiguring buildings over their life cycle. They are concerned with potential “demand side” aspects, which is where any business-plan should start. The following points focus on the “supply side” and how that may evolve.

Reducing the carbon footprint Much of the focus to date has been on how to improve the energy performance of buildings in use. Offsite construction has been demonstrated to offer improved performance in terms of construction quality assurance and the ability to create buildings with very good air leakage performance. Embedded carbon has been a bigger challenge. Overbuild requires substantial structural supports that are going to require concrete and steel in significant quantities. Reduced carbon concrete, for example using low carbon energy sources and increasing proportions of recycled materials, such as GGBS, is increasingly being used. A new family of alkali-activated cementitious materials (AACMs) are now becoming available. Buildoffsite’s members C-Probe Systems (LoCem) and Lucideon (MIDAR) have taken low carbon materials development further, as has DB Group (Cemfree). Some of these products claim to reduce the carbon content in concrete made with them by -80 to 90%. There are at least five such AACM formulations becoming available in the UK for a variety of build mix designs, for example for foundations and precast elements, as well as the integration of AACMs with Portland concrete constructions to incorporate resilience to such structures. In 2016, BSI published PAS 8820 to facilitate the specification and use of such materials. Professor Paul Lambert of Mott MacDonald has stated that alkali-activated cementitious materials represent a family of alternative binders that can be employed as full or partial replacements for Portland cement in mortars and concretes and are able to provide superior performance in a number of key areas. AACMs gain strength through the reaction between an alkali (often an alkali silicate solution) and an aluminate-rich material such as fly ash or blast furnace slag. Unlike traditional Portland cement-based materials, the structure of hardened AACM does not rely on hydrates, making them much more thermally and chemically stable - some AACMs are also referred to as “geopolymers”. While the low-carbon credentials of AACMs are excellent and should be sufficient to encourage their wider use purely on the grounds of sustainability, the superior resistance of some formulations to extremes of temperature and aggressive chemical environments has resulted in early adoption for niche applications where fire and acid resistance have been essential. Fire-proof lintels and sewer linings are but two examples of recent applications where conventional systems would have proved significantly less effective. Guidance on the specification of AACM mortars for use in construction-related applications is available in PAS 8820 ‘Alkali-activated cementitious material and concrete – Specification’, published by BSI.

Improving fire resistance

Et parisciis aut faccusa

As mentioned by Paul Lambert above, AACMs are also applicable to refractory applications where high fire and thermal resistance is integral to their chemistry and rheology as alumina-silicates. One company’s testing shows resistance of 150mm thick precast slabs up to 1200C for 5 hours with no change to form and only 140C temperature rise on the unfired side (compliance with EN1363-1). Such performance can be put to good purpose with rail overbuild applications, especially for the rail encapsulation structure. Opportunities therefore exist to reduce the thickness of precast elements but retain resilience to load, fire and corrosion, while reducing the carbon footprint. Lucideon are also focusing upon reducing fire risk in offsite construction systems. There may be a noncombustible approach coming through development, that could completely eliminate the risk of fire in the


structural and thermally insulating parts of a home, leaving just furnishings as the potential fire source. Lucideon has been developing such an approach using its geopolymer technology, ‘MIDAR’, alongside a very forward-looking client over the last 12 months. Extensive progress is being made and the project is now at phase II, where engineering processes, weight and cost reductions are being targeted, and the appropriate testing of panels is underway. The material is dense, has excellent sound attenuation, and thus could be used in sites where noise could be a nuisance, for instance, close to railway lines. Such a material may also have good vibration minimisation benefits. Lucideon suggests that the material under development could be used to manufacture non-combustible structural insulated panels (SIPs) in a factory close to the construction site. Furthermore, the materials used would be low cost with a low to no heat process, and hence be energy efficient and have low carbon emissions.

Figure 5.5 MIDAR structural insulated fire-proof panels Image ©Lucideon

The thermal mass of a large concrete structure offers the possibility of it being used to store heat or coolth depending upon the season to aid in achieving energy targets for the overall development. Concrete in general absorbs small amounts of carbon dioxide during its life cycle, however this carbonation process is one of the mechanisms that causes corrosion and early concrete repairs and maintenance in concrete structures if other corrosion resilience technology is not incorporated.

Designing for resilience Design for resilience of structures takes many forms, including environmental, wind/movement, chemical, load and so on. One of the main environmental effects is corrosion of the reinforcement steel within the concrete cover that adds to future maintenance cost and disruption to use of the rail network. Measures can be taken at the design stage to build indefinite resilience to corrosion in from the start of the process by considering solutions aimed at assuring the bond between the steel and the concrete interface using the application of controllable current from impressed current cathodic protection (ICCP). This provides external control of the future of the structural integrity of the reinforcement steel and, as a consequence, the resilience of the concrete cover. C-Probe Systems has used LoCem to provide such controllable resilience systems in the form of ICCP concrete within precast structural elements to ISO12696:20161.

1 (ISO12696:2016 Cathodic protection of reinforced concrete; And O’Flaherty et al, Optimising cathodic protection design for maximum bond performance in reinforced concrete, Materials and Corrosion 2018, 1-12)


The internet of things - Structural health monitoring and care Adding measures as described above offers wider significance given that external control of future resilience of infrastructure requires intelligence to be cast into the structure with data produced for such control measures to be made. This significantly reduces the cost and risk of future infrastructure disruption through the need to repair1. C-Probe Systems and sister company Structural Healthcare Limited has developed these measures in the form of embeddable sensors for performance assessment, remote online control of ICCP systems and service life tracking that can be provided on open network architecture to allow additional functionality to be integrated on the same network.

Figure 5.6 Image ŠC-Probe Systems Ltd

This allows expansion of functionality enabled from monitoring and control innovations; the Internet of Things. These can take many forms such as simple lighting controls giving efficiencies to energy use and safety or innovative neural network learning of the behaviour of people and vehicles that use the transportation infrastructure. This learning can then improve and influence future management decisions while minimising societal impact of travel.

1 (BRE Digest 455 Corrosion of steel in concrete: service life design and prediction; ICE proceedings, Jones and Lambert, Predicting service life from site accessed corrosion rate data, April 2016) (BRE Digest 455 Corrosion of steel in concrete: service life design and prediction; ICE proceedings, Jones and Lambert, Predicting service life from site accessed corrosion rate data, April 2016)


New standards for modularization Standards can be a driver and enabler of innovation. An example of the first has been Building Research Establishment’s BREEAM standard for sustainability assessments. An enabling standard has been PAS 8820:2016 for the new family of low carbon AACMs and related concretes. BSI, funded by the Government, has just completed a research study with Loughborough University to identify where standards may be improved or created to improve offsite construction, so more can be expected in this area in the coming months and years.

Figure 5.7 Image ŠBSI There is already a move to standardise the templates for multi-floor residential buildings and the interconnections between different types of offsite modules. The Manufacturing Technology Centre (MTC) in Coventry is working with the industry to develop an approach, with Innovate UK backing, to deliver a step change in construction productivity and the opportunities for combining modules from a range of suppliers. BSI is working with HTA, architects responsible for multiple high-rise modular buildings, and others, to create a PAS (publicly accessible specification) for the design of such structures. Again, the aim is to ensure that lessons learnt to date are shared and taken advantage of in future projects.


Figure 5.8 Apex House, student accommodation buildings in Wembley, developed by Tide Construction and Vision Modular Systems,designed by HTA Design LLP, illustrating both scale and constrained site working. Image ŠVision Modular & Tide Construction.

3D scanning and the positional accuracy of construction assembly Dimensional accuracy, whether in a measuring or manufacturing capability, can result in gains in speed and material construction productivity. Components fit first time without adjustment. Accurate materials quantities can be ordered and delivered. Efficient setting out strategies can therefore make a significant impact upon project duration and cost.

Digital based processes - BIM and the automation of design and construction Much has been written about how BIM enables efficient design and the transfer of specification information onto manufacturing-based suppliers. It also enables the virtual sequencing and optimization of the build (or assembly) process. As advances are made in the areas of construction robotics and materials handling, this is likely to increase further. Et parisciis aut faccusa Rule based design processes can also be exploited when working with different types of modularity and in areas where experts are not employed in all design practices. Such systems may deliver 80% savings in design resources required to configure an offsite system for a project.


Figure 5.9 The incorporation of rules based design into an offsite production facility’s information flow, Image ŠBerkeley Modular and DAS

New manufacturing processes Large scale casting (including slip form) is well established in construction. Extruding materials is also well established. Materials and equipment are now becoming available for 3D printing (additive manufacturing), which is making cost-effective creation of complex geometry more feasible both on sites and in factories.

New assembly processes Offsite specialists are regularly improving their assembly processes, often eliminating aspects such as the need for temporary works and scaffolding. However, in this environment, it is essential that the infrastructure that is being built over be protected, particularly from falling objects. Buildoffsite member Mace have worked with Castle Scaffolding who have produced a netting protection system that significantly reduces the number of rail possessions and night-time working required during a project. The system is fitted at ground level and telescopes upwards above the working area, creating a complete safe working zone separating the operatives and materials from the public and infrastructure. The netting forms one complete curtain for operatives to work behind from ground level upwards. Each level is then fitted and the system moved up to suit the progression of the build. The reverse process is applied for dismantling. The system is currently being used on the construction of a new station at Twickenham.

Figure 5.10 Innovative safety netting system used at Twickenham Station Image ŠCastle Scaffolding



Stakeholder approvals Overbuild projects are likely to involve multiple stakeholders, each with their own requirements and approvals processes. Significant project time savings may be achievable if such stakeholders agree at the outset to have a shared approval process.

Optimizing value by reducing elapse time (and related costs) Buildoffsite member Lean Thinking Ltd. has designed a new project delivery system called APD (Accelerating Project Delivery). The system focuses on compressing time as the most effective way to optimise value. Time can be related to 80% of the project cost. The system accelerates projects’ completions by dealing comprehensively with complexity and time related risk and uncertainty, utilizing a number of fundamental approaches such as: • • • • • • • • •

Systemic/holistic view – appreciation of the interdependencies Systems thinking: The focus must be on the system i.e. the hourly, daily and weekly routines rather than the outcome. The quality of the system determines the outcome Horizontal accountability and collective intelligence/wisdom at all levels Constraint management and prioritisation Short feedback loops and scientific daily calculation of time to completion (akin to how a sat. nav. works) One-piece continuous flow Digitisation and artificial intelligence Parallel processing onsite and offsite Intrinsic motivation – engagement and involvement of everyone at every level with problem solving and improvement of the system

This system and the fundamentals need to be in place in full at all project stages, including offsite manufacturing, in order for the client to experience optimum value. When these fundamentals are focused together on time compression and applied collectively in fixed daily and weekly routines, visibly and at all levels, they will transform project performance. Lean Thinking suggest from close to 80% running over time and budget (Oxford SBS) to over 80% ahead of time and cost.

The use of consolidation/logistics centres Major programmes such as those at airports and for the Olympics have demonstrated how useful logistics and pre-assembly facilities can be in delivering offsite solutions efficiently and enabling just in time deliveries in the challenging construction context.

Horizontal packaging of mechanical and electrical services Often plant rooms are located high on buildings. However, with planning height limitations and the challenge of repairing and replacing equipment at height, the possibility of using otherwise unused spaces in the supporting structure (as mentioned above) for the placement of mechanical and electrical plant and their horizontal distribution could be exploited.


Reducing weight of components Reducing loads on structures can result in reductions in the foundations and in the strength needed for supporting structures. The use of offsite systems can often contribute to this. Examples could include lightweight cold rolled steel or timber frames or structural insulated panels in volumetric or panellised construction systems, with the incorporation of other major light weight elements such as pre-manufactured, standardised, steel frame lift shafts. Another area of weight saving and futureproof opportunity is with lightweight, decorative, over claddings which are individually removable and ideal for maintenance, access, and ongoing inspection of the structure behind. One such product developed by Tata steel and Reform includes finishes such as Prisma coated steel, Skin rock and brickslip.

Figure 5.11 Image ŠIdeal Lifts


Sustainability analysis


Building over linear infrastructure, particularly close to transport connections such as railway stations, urban motorway junctions or park and ride sites, can bring many benefits in terms of sustainable development.

Definition of sustainability Sustainability involves the simultaneous pursuit of economic prosperity, environmental quality and social equity. Sustainable construction needs to perform not against a single, financial bottom line but against this triple bottom line1. Close connections of public transport options significantly reduce the need for individual car ownership. The creation of new communities and connection of them to others that have been separated by railway lines or major roads can create economic scale for the provision of a range of local facilities, such as retail services, education, sports or healthcare centres, entertainment and green spaces. This further reduces the need for individual vehicle ownership and can contribute to all parts of the “triple bottom line”. The Buildoffsite report ‘OFFSITE CONSTRUCTION: Sustainability Characteristics’2 used the definition above and concluded the following: Offsite construction has many attributes to commend it from a sustainability point-of-view. The arguments presented in this report are overwhelmingly positive. Indeed, it is difficult to find any aspect of offsite construction, which has a negative implication for the sustainability case. Given the strength of this case, it might be considered odd that offsite methods have not achieved a greater presence within the construction industry. It is the view of the authors that the reason for this lies in the fact that the benefits arising from the sustainability case bring no direct advantage to the developer or the building contractor - the key decision makers at the time when construction methods for a project are defined. This point is illustrated in the table below, which sets out the main sustainability arguments examined in this report and attempts to identify where the main benefits arise and accrue. Referring to this table, the following key points should be noted: • •


Offsite construction has a very wide range of sustainability benefits, some of which are coupled with significant financial benefits. In cases where the financial benefits accrue to the developer/builder, it might be expected to influence the decision to adopt offsite methods for construction. However, the power of this influence depends on degree. The biggest financial benefits (by far) arise from the increased speed of construction, which brings about reductions in construction programme duration and consequent reductions in financing costs. There are also significant cash-flow benefits to be had in terms of early completion and consequent early sale/rental income. Beyond those issues identified above, many of the financial benefits estimated here are relatively small when measured as a fraction of the construction value. Their degree of influence over the choice of construction method is therefore unlikely to be significant.

Based on the definition adopted by the World Business Council

2 ‘OFFSITE CONSTRUCTION: Sustainability Characteristics’, Buildoffsite June 2013 authored by Daniela Krug and Professor John Miles

Lead Editor Nigel Fraser, Buildoffsite


Issues of access and servicing are common to most railway sites suitable for overbuild development, many of which are characterised by varying edge conditions. These include borders with domestic gardens that are sensitive to overshadowing and overlooking, or the stark facades of industrial units. The boundary conditions do not always provide an attractive aspect for high quality new developments. An architectural response to this unlocks the development potential of such sites by using the new platform over the railway as a street. This street does not need to have vehicular traffic. It may need to be narrower than a suburban road due to the width of the rail land, and could be better conceived as a strip park that incorporates pedestrian walkways and cycle routes. This concept generates an appropriate focus and outlook for the residential buildings. At the same time, it provides a new transport network or leisure promenade at the heart of the scheme to facilitate the connection of previously divided neighbourhoods. The buildings on either side will frame the central route, and thus cores will most sensibly be located to each side of the railway lines. This arrangement helps to reduce load transfer. In certain conditions, it also allows direct access to the lifts from ground floor level where the railway is also at ground level. A plan illustrating this approach is shown in Figure 3.3 and the corresponding section in Figure 3.4.

Figure 6.1 A newly reconnected neighbourhood over rail tracks to the east of Gare d’Austerlitz in Paris Image ©WSP

There are some offsite sustainability benefits that are difficult to express directly in terms of general percentages of construction value, but which, nevertheless, are very powerful commercial factors. These include: •

Early availability of the finished building – early sale/rental streams have been mentioned above, but there are particular benefits for certain classes of building that can be even more influential. Examples include air-side buildings at airports, where the value of time is greatly magnified because construction disruptions can have huge adverse effects on the primary revenue-generating operations of the client, and ‘imperative’ buildings in the public sector, for example prisons and hospitals. Higher EPC/DEC/BREEAM ratings - the value of a good energy/ sustainability rating can be significant when determining the commercial value of a finished building to a property developer.

In summary, it may be said that the ideological and commercial benefits of offsite construction are numerous. Depending on where the financial benefits accrue, these factors can be expected to influence the choice of building method. In cases where the construction cost, operational costs and time benefits all accrue to the same party, for example owner/occupiers or the private rented sector, the case for adopting offsite methods is particularly compelling.


Figure 6.2 Sustainability and Offsite Category/Attribute

Potential improvement over conventional construction

Societal benefit

Financial Benefit to Builder/Developer



Health & Safety

Up to 80%



H&S is a critical operational factor for the builder/ developer, but it is not appropriate to record a financial benefit under this heading

Improved working conditions




Improved working conditions in the factory have little effect on the builder/developer


Small (Less than 1% of construction value)

Improvements shown in paranthesis are net figures making allowance for factorybased traffic movements Improvements shown in parenthesis are net figures making allowance for factorybased energy consumption

ENVIRONMENTAL Reduced road traffic movements

Up to 60% (20%)

Reduced energy used on site

Up to 80% (30%)


Small (Less than 1% of construction value)

Reduced waste

Up to 90% (50%)


Significant (up to 2.5% of construction value)

Improvements shown in parenthesis are net figures making allowance for factorybased wastage


Financial savings from reduced energy-in-use are not a motivator to the builder/ developer (except where the builder/developer is also the operator/occupier of the building)

Benefit realised through reduced project financing costs

Reduced energy-inuse

Up to 25%


ECONOMIC Faster construction

Up to 60% reduction in onsite construction programme


Large (up to 8% of construction value)

Improved cash-flow




Reduced snagging & defects

Up to 80%


Significant (up to 2% of construction value)


Health and safety This subject is not negotiable and is a major focus in the chapter on railway “asset protection”. It is worth noting, however, that traditional construction sites are generally considered to be 2 to 2.5 times more likely to have accidents than typical manufacturing factories1. Taking 70-80% of the work away from an overbuild construction site into factories is likely to lead to a significant improvement in safety for those involved – a significant consideration for overbuild projects. In the specific context of overbuild, there is also the evident reduction in the number of items (tools and materials) that need to be tethered during use or assembly. There is also the opportunity to remove, or at least substantially reduce, the need for scaffolding and the associated inspections. By creating a deck on which to assemble the superstructure, a safe operating environment can be established for the operational infrastructure beneath at an early stage.

Improved working conditions Working in the vicinity of linear infrastructure often increases the difficulty of tasks, whether it is above railway lines, roads or waterways. Offsite working reduces the amount of this – lessening the need to work at height in harnesses or working trackside are just two examples. The general benefits of working in a factory environment, protected from adverse weather and working safely and close to home apply to all offsite factory-based production.

Reduced road traffic movements The precasting of concrete, prefabrication of steel structures and panelised and volumetric modular construction systems reduce the number of material, waste and labour transport movements, although it may increase the size of some of the vehicles, notably mobile cranes and low loader articulated lorries.

Waste The management of waste can be a major issue when it comes to building in a confined space. Offsite construction has been demonstrated to have a significant impact on this by only delivering to site that which is needed. In addition to this, waste levels in factories have been demonstrably reduced as many components are manufactured to fit without further cutting or shaping, quantities are more easily measured accurately and what waste there is can often be recycled.

Energy The amount of energy embedded in traditional structures is significant, whether they be made of concrete, steel or a combination of the two. However, the offsite sector is accustomed to re-using steel and is increasingly using reduced carbon concrete mixes in the creation of precast beams, walls and decks. This trend is likely to progress further with the use of alkali-activated cementitious material-based concrete (see chapter on innovation). In addition, the use of impressed current cathodic protection around vulnerable points in a reinforced concrete structure may significantly reduce maintenance and facilitate inspection, particularly when combined with networked corrosion management systems, or structural health care. This in turn reduces the future risk of a requirement to deconstruct and recycle the structure as low value crushed concrete. With respect to in-use energy consumption, factory-built modules are capable of being sealed with tight control of air leakage, which has been demonstrated to reduce energy consumption. The additional energy used in active corrosion management systems mentioned above would be insignificant, because this happens at the molecular level and requires very small currents to be effective.

Economic In the context of overbuild, the economic benefits are derived from both the shorter development period and the significant reduction in non-value added activities related to rework and waste. Offsite methods are also likely to make more schemes economically viable where access and possessions, for example of railway sites or motorways, is very restricted, expensive or risky for traditional construction methods. For all of these reasons, offsite construction can play a major role in improving the sustainability of overbuild projects.


HSE report into health and safety in construction 2013 and HSE report into health and safety in manufacturing 2013)


Global overbuild initiatives and expertise Linear infrastructure overbuild has developed over many years and indeed ever since the particular infrastructure was planned and constructed. Linear infrastructure is always about transport corridors in the form of rail or roads. These transport solutions are reflective of economic growth, stable governance and the desire to join towns and cities together to create larger communities and networks.

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It’s important to add that the opportunities are greatest in our mature cities where rail systems were introduced gradually as rail technology and the desire for this type of travel expanded. In the UK this means looking back to 1850 and the industrial revolution. Over time, stations in the larger cities, expanded and communities became divided by the widening rail corridors. Of course, those same communities were able to travel quickly and safely into the centres of cities, as well as get to other towns and cities. These rail corridors were often acquired through government legislation and compulsory purchase arrangements. The same approach applies today and the amount of land consumed in this way is extremely large. The land typically affected is also in areas of desirable densification and frequently close to a station. This proximity to a station is turning out to be significant in reducing the reliance on cars, improving air quality and encouraging the use of public transport, walking and cycling. This trend and change in public transport provision has taken place on a global scale in the most prosperous countries and their key cities. This chapter describes some recent research carried out by WSP on a range of mature global cities, identifying the quantity of land potentially available. The chapter also discusses the ways in which overbuild has evolved in different locations and some of the drivers for this form of development. Recent and current examples of overbuild are highlighted and in addition, some of the different methodologies and asset protection regimes are discussed.

Lead Author

Figure 7.1 Map 1 – Borough boundary It includes three extracts from the maps generated, zooming in from the whole of a borough to specific track locations.

Bill Price, WSP


Figure 7.1 Map 2 – Local boundary

Overbuild research In 2018, WSP carried out a study of overbuild potential in London. The study title was ‘Out of Thin Air’ and it measured all the land area in use by train and tube lines. A simple calculation was then applied where it was assumed that if only 10% of this land could be developed for housing (a home unit being 100m2) to a height of 12 storeys, then 250,000 homes could be delivered. This, at the time, was 5 years’ supply at the level of demand identified in London. This ‘discovery’ generated considerable interest both from the rail stakeholders as well as developers, local authorities and central government. In 2019, further analysis work was undertaken to identify the most likely locations for such housing. The methodology involved superimposing further layers onto the basic mapping to focus on: • • • •

Opportunity areas Proximity to a station Not being too close to listed buildings or in a strategic sight line Existing population density and house prices

In Figure 7.1 Maps 1, 2 and 3 output is shown from the 2018 study gradually zooming in on preferred locations along the rail corridor.


Reducing the carbon footprint Figure 7.1 Map 3 – Local boundary In London, the map shown in Figure 7.2 was generated to indicate the hot spots for prioritising further investigation. The track with most potential by the criteria identified is highlighted red and the least suitable is light grey. It remains critical, however, to examine specific sites using satellite mapping and a site visit if it looks promising.

Figure 7.2 – Greatest suitability zones for new homes in London The work undertaken for London has generated interest on a global basis for this digital, data-driven approach to establishing the housing potential of this type of land. It should be noted that London is a large, mature city and it is often considered to comprise the 32 local authority districts. Geographically this is a roughly circular zone with a radius of around 20km. In order to create a more realistic overbuild comparator Et parisciis aut faccusa for other (smaller) global mature cities a radius of 10km has been used in Figure 7.3.

The overbuild study has been carried out for the 11 locations identified and some are possibly surprising. For example, Australia has a great deal of land available but in Melbourne there is great pressure to build new homes and drive regeneration, whilst improving air quality and reducing numbers of cars.


City (0-10km)

Units (incl. 10%) 12 storey, 100m2/unit

Hectares of rail land (incl. 10%)
















New York


















Figure 7.3 – Global cities’ potential for homes over rail (10km radius)

The global themes coming through all these studies about overbuild are as follows: • • • • • • •

The land is usually in quasi-public ownership; The land is fundamental to the operational rail systems but can offer ‘air rights’; Sites want to be ‘repaired’ in some way and not be scarred by the linear rail corridor; Most cities wish to densify holistically by providing homes, employment and amenity; Cities want better air quality through diminishing car use; Cities want more income (tickets/fares) from the use and expansion of rail transport; Some cities see these corridors as able to provide much needed green space and landscape.

Case studies and examples New York, Paris and London have a long history of developing over rail infrastructure and typically at or close to rail terminus stations. Good examples from the latter part of the twentieth century include Grand Central and Pennsylvania Stations in New York. In London, Liverpool Street and Charing Cross are well known landmarks. In Paris there has been ongoing work by Semapa at Paris Rive Gauche, together with other locations. More recently in New York the 14-acre Hudson Yards site has seen 19 million square feet of commercial, residential and mixed-use development. Other New York projects include the World Trade Centre, Riverside South, Atlantic Avenue, Moynihan East and Sunnyside Yards at Western Queens. In all instances, major buildings have been constructed over the challenging rail environment to create significant value concentrated on a transport hub. These projects are technically complex and very successful. In some cases, however, things are more difficult. Sometimes the business case dominates the scene and schemes fail to materialise. The usual failure points comprise: • • •

Decking costs being too high (span width, special foundations, etc.) Rail restrictions creating risk and uncertainty Extended programme periods associated with approvals and possessions

In the cities mentioned above and especially in New York, the economic climate has improved significantly. At the top of the residential market, New York is regarded as a leading investment location, attracting large quantities of overseas as well as USA-based funding. The overall profile and prosperity of New York is also generating population growth, which in turn is creating housing demand of more than 25,000 homes per year for the next 20 years. These same points apply to London and Paris, where similar prosperity and growth issues are occurring. These factors have created the conditions where the task of rafting over rail assets is increasingly seen as attractive: viable in the sense that the deck costs are in better proportion to the overall development value and attractive because the commercial benefits to the rail asset owners can be reinvested in the infrastructure the city needs.


Clapham Junction, London



Network Rail own the majority of the land here and are likely to form a JV arrangement with a developer. The site currently Precast, prestressed bridge comprises beams are arecommended to suit rapid assembly within the mixture of through tracks, switches and extensive constraints of track closures. They can efficiently span the track arrangements shown in stabling. and access to infill and topping concrete. Attention should be FigureFacilities 2.2, and for cantravellers be combined with in-situ thepaid 17 platforms is poor throughout. This is a to deflection limits specified by the manufacturer of modular overbuild components. very large scheme and the intention is to deliver a new station for this criticalwith interchange to the slabs are likely to be the optimal solution for the Beams placed together in-situ topping west of London. If Crossrailand 2 progresses, shorter span structures structures this carrying less onerous loading. Deeper downstand willbeams, add further to the transport provision thein-situ concrete topping slabs are likely to be the placed at much wider centres,of with location. preferred approach for structures with longer spans and heavier loading. The beams should be positioned directly below concentrated loads. This transformation would all take place in sequence to and optimise the construction Reducing distributing loading onworks the deck as far as possible is preferable and will andminimise minimisethe disruption travellers. Above the and foundations. Loading can be reduced by size andto cost of the deck, walls station could be a large mixed use, residentialfavourable massing of buildings on the site, adopting lightweight modular systems and by ledconsidering regeneration to create lightweight a new district or specifying concrete. neighbourhood. There will also be benefits in terms linking communities to the north and depths for a lightly landscaped podium and six Figureof2.3 indicates typical deck sections andand south across the construction large transport twelve storey of corridor. either volumetric modular or traditional RC frame. For the Project feasibility studies were undertaken in longest and most heavily loaded span considered, a shallow deck is achievable, but deeper 2018/2019. Progress planning application downstand beamswith are apreferable to be structurally move efficient. is only expected to proceed if there is general acceptance valueprecast generating overbuild Figure 2.4of shows beams with an insitu topping being at Twickenham Station, Figureinstalled 7.4 - Clapham Junction, London density andinmore London 2018.certainty around Crossrail 2. Map data: Google, Maxar Technologies

Gothenburg, Sweden


The area in question is to the north of the existing main station and close to the Gota River. In this location, a major dual carriageway motorway has been placed into a cut and cover tunnel around 1km long. The road was previously at grade and helped to cut off the attractive river side from the historic town. The lid of the tunnel will be used for new landscaping, offices, residential and retail, thus creating a large new district in the heart of the city. Air quality and environmental acoustics will also be improved. The works are progressing and the highway changes should be complete in 2020.


Et parisciis aut faccusa

Figure 7.5 - Gothenburg, Sweden Google, Maxar Technologies Figure 2.3 Precast, prestressed deck: typical deck depthsMap anddata: sections (image courtesy of WSP/Shay Murtagh).



Hudson Yards, New York

This site is located on the west side of Manhattan at the northern end of the High Line and lies between 10th and 12th Avenues and West 30th to West 34th Street. An entire new financial, tech, retail and business district has been constructed over the last 10 plus years, including a new subway stop on the No. 7 line, which opened in 2015. Huge density with several buildings well over 50 storeys has been delivered alongside public parks and amenities. The stabling (yards) beneath has all been retained together with other critical rail functionality. This is perhaps the best current global example of rail overbuild generating value and turning a once ‘industrial’ area into a dynamic, connected district in the heart of New York. The site will approach completion in 2020.


Figure 7.6 - Hudson Yards, New York Ore pre exerum Accatemolupta necepedit Map data: Google, Maxar Technologies quas a conseque et lis etus. Quianis dolorio restrum quid est aut aute ped eum ad quaspient. Esedictem eum repere apissimus andam nihicias ma quas Ny Ellebjerg, Copenhagen doluptas aliat.

This site is situated to the south west of the centre of Copenhagen in Denmark where several different train lines converge, with a metro station to be added by around 2024. Metroselskabet is investigating an overbuild for the area in order to facilitate improved interchange for travellers, provide new homes close to the transport hub and to connect communities across the wide rail corridor. Metroselskabet is also interested in ensuring that the new metro station box is designed to accommodate overbuild in the future with the minimum of disruption. The master planning stage should commence in 2020 where development options and planning will be considered further alongside rail constraints and opportunities.

Figure 7.7 - Ny Ellebjerg, Copenhagen Map data: Google, Maxar Technologies


Peripherique, Paris


The Paris inner orbital road system was constructed in the 60s and 70s and remains a fundamental part of the road transport network. Much of the route is in a cutting and very close to dense neighbourhoods and other transport infrastructure. In recent years several areas have been given a lid or deck. These areas are often used for public realm, parks and sports facilities. This has had the effect of improving the connectivity of communities and reducing air pollution and acoustic disturbance. The geometry of the original cuttings has meant that the decking has been relatively achievable in most of the locations undertaken so far.

Figure 7.8 - Peripherique, Paris Map data: Google, Maxar Technologies

Rive Gauche, Paris


The Rive Gauche site has been gradually developed over the last 20 years. The zone is a collaboration between the City of Paris and SNCF, custodians of the rail land. The development entity is known as SEMAPA and the rail lines mostly feed Gare d’Austerlitz, which is located about 1km further west. Working from the eastern end of the site, this large tract of rail land is now largely overbuilt. The rail lines are roughly 6m below the road level to the north and at grade with streets to the south. The transfer deck effectively extends the higher (northern) ground level towards the south by around 70m. The deck is supported typically on long wall elements to help reduce the span (and hence the depth) of transfer beams. The deck, which is currently around 1000m, long supports offices, residential, retail and public realm. A new road crossing has been formed and level differences for pedestrians overcome with stairs, escalators and lifts. The deck comprises a mixture of precast beams, steel plate girders, trusses and hybrid elements to suit specific rail conditions. The rail is overhead electrified and there are a number of switches and other critical elements of rail infrastructure. There is no station below the deck. New buildings above are mostly in the region of 12 storeys high and the project is one of the best city overbuild developments in the world.


Figure 7.9 - Rive Gauche, Paris Map data: Google, Maxar Technologies



Royal Mint Gardens, London

The Royal Mint Gardens site is located to the east of the City of London, close to Tower Bridge. The rail situation is indicated and shows the elevated Network Rail track and Docklands Light Railway (DLR) in the right foreground as it emerges onto the surface from the tunnel. The Royal Mint Gardens project consists of a 14-storey high mixed use development. The development is constructed over: • The main lines into Fenchurch Street Station; • The high level DLR line to Tower Gateway Station; • The low level DLR line to Bank Station Transfer structures in steelwork, rail encapsulation in precast concrete and isolated foundation solutions overcome acoustic and vibration issues. The residential development is fully isolated from DLR and Network Rail vibration with neoprene pads located beneath all columns and cores. The new buildings also accommodate ventilation shafts for the DLR as the ‘tunnel’ environment is extended by almost 150m. The residential development is expected to be complete in 2019 and occupied in 2020.


Figure 7.10 - Royal Mint Gardens, London Map data: Google, Maxar Technologies

Ore pre exerum Accatemolupta necepedit quas a conseque et lis etus. Quianis dolorio restrum quid est aut aute ped eum ad quaspient. Esedictem eum Principalrepere Place,apissimus Londonandam nihicias ma quas doluptas aliat.

Principal Place is a 50-storey premium residential tower development and is situated on Shoreditch High Street, near Liverpool Street Station in Central London. Brookfield Europe implemented this major project to develop land adjacent to an open section of the railway, approximately 200 metres north of Liverpool Street Station. Figure 2.4 Precast beams being installed to support overbuild development, Twickenham Station, London. Courtesy of Banagher Precast Concrete. The scope of the first phase of this project was to cover the open ‘cutting’ with a steel and concrete deck. This enables pedestrian access across new public realm to future phases of the development just to the south of the residential tower development. Most of these challenging works required night and weekend possessions and closures coordinated with planned changes to Network Rail’s own infrastructure. Consequently, precise programming and collaboration were crucial to the efficient and timely execution of the works.

Figure 7.11 - Principal Place, London Map data: Google, Maxar Technologies



Sunnyside Yards, New York

Sunnyside Yards is located in Queens, New York City, to the east of Manhattan. A team comprising key stakeholders, designers, master planners and engineers has completed a feasibility study for the site. The study provides guidance to the City, Amtrak and the community of Queens on the viability of a mixed use overbuild development. The Yards currently provide nearly 1.75 miles of active rail use for a range of transport stakeholders including Amtrak, MTA/LIRR and NJT. The overbuild development vision could potentially support 180 acres of additional residential, retail, community and commercial properties. The project is in line with the 2014 Housing NYC Plan, which calls for the city to determine the feasibility of decking over rail facilities to support affordable housing and foster liveable, diverse neighbourhoods through mixed use development. A range of structural solutions to address a large variety of rail infrastructure and overbuild density options have been identified. These include long span steel trusses, precast beams, concrete wall elements, vibration isolation, transfer columns and installation of foundations close to operational rail corridors. A key consideration has also been the ground level differences surrounding the very large plot and how new public realm, roads and strategic access points can be enabled in the completed masterplan.

Figure 7.12 - Sunnyside Yards, New York Map data: Google, Maxar Technologies


Summary It is clear based upon current activity around the world that the opportunities associated with the overbuild of linear infrastructure are being realised. The majority of projects are in city locations where property values are high and there is proximity to a station or other significant transport node. The example sites and overall land opportunity research described above convey the progress made and shared ambition in a range of global cities. The nature of the overbuild development varies considerably depending on the factors already discussed in this guide. It is clear, however, that a general global theme is the strong desire for housing to contribute to city density and take advantage of the air-rights associated with land in typically quasi-public ownership. It’s also clear that global transport infrastructure stakeholders are being encouraged to facilitate this form of development. It’s no coincidence that more people using public transport helps fund the infrastructure, and if there is reduced reliance on cars there are benefits for air quality and wellbeing. The continuing global development of this land is helping to deepen understanding of building methods and systems in the context of safe, secure and continuing rail (and road) operations. Companies with construction, design and manufacturing skills in conjunction with global reach are well placed to take advantage of this growing market if they can collaborate and communicate effectively.


Ownership models and procurement

Ownership Models

8 1

The ownership model will depend on the asset owner and developer. Network Rail discuss two development models in ‘Development: Open for Business: land disposal and partnering’: “We prioritise direct developments, joint ventures and partnerships over land disposals to ensure we maximise value and deliver real improvements, such as enabling the delivery of new homes and the creation of jobs.” The Twickenham project was constructed by Solum, a partnership between Network Rail Property and Kier Property.

Figure 8.1 - Computer generated image of Twickenham Station redevelopment, extracted from ‘Unlocking land for homes London’, Network Rail Property, September 2017

Lead Author Patrick Hayes, Meinhardt


Trackside land tends to be disposed of and the revenues returned. Transport for London (TFL) operate similar models. For oversite development, the asset owner may either act as a development partner or lease air-rights. The decision will be mainly determined by the asset owner. Both Transport for London and Network Rail take a flexible approach, the latter noting in ‘Unlocking land for homes London’: “In some instances, joint ventures work best. In others, our role may be to make the site development ready and work in partnership with the developer to create the right scheme. And on occasion, we may sell the site directly.” The final model depends on best value to asset holder, physical proximity between developments and development complexity. These considerations are summarised in Figure 8.2. Adjacent Land Land Disposal


x x

Air-Rights Long Lease JV/Partnership





Figure 8.2 Land type and development ownership matrix

Air-rights model In this model the asset owner leases the air rights over the asset (tracks). The encapsulation system may revert to the asset owner or remain with the developer. In the former case, an annuity or ground rent from the developer to the asset owner is required to cover annual maintenance. In the latter case the developer would pay the asset owner an annual fee to maintain the structure. The transfer deck and superstructure are owned by the developer. In this model there would usually be a legal agreement between the asset owner and developer setting out obligations on either side. In the case of Network Rail this is a Basic Asset Protection Agreement (BAPA). Examples include the Bishopsgate development and Royal Mint Gardens. This approach is described in The Hansford Review for “Type F & Type G” projects.


Figure 8.3 Network Rail third party development model, taken from the Hansford Review

Partnership model This tends to be the preferred Transport for London model. In this model, Transport for London enter into contract with a development partner. The proposals should generate net value. Transport for London meet their objectives of providing affordable housing through the development, as well as providing commercial space. Transport for London’s preference is to retain a development stake to ensure management of the development does not compromise the asset. In this model it is again assumed that the encapsulation is maintained by the asset owner. The costs of this therefore need to be amortised. The developer takes the lead. Examples include Earls Court and North Greenwich station. In all models there is an underlying principle that the development should deliver net land value.

The delivery approach General approach Given the complexities and risks associated with overbuild, a structured approach is required to sequentially assess feasibility, value and risk. It is fundamental that a risk management system is put in place. This needs to identify the stakeholders and their priorities and be compatible with the asset owner’s own procedures. In terms of de-risking, Transport for London and Network Rail have established procedures for constructing over and around their assets. Following these procedures goes a long way to mitigating the operational risks. The objectives can then be categorised by stakeholders and the risks then assessed by project stage.

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Figure 8.4 Stakeholder objectives


Development stages The approach outlined below aligns the RIBA project stages, which apply to the over-station development, with Network Rail’s GRIP development process, which covers work affecting the asset. 1. 2. 3.

Categorise projects in terms of operational complexity Rank in terms of development viability Develop a staged approach to the roll out of the strategy based on RIBA/GRIP

Ideally steps 1 and 2 would be undertaken by the asset owner, to allow interest to be solicited from the market. Part of step ii would be assessing the planner’s views on the development acceptability. Step 3 would be carried out by the asset owner and developer in conjunction. This approach is followed by both Transport for London and Network Rail, with both carrying out feasibility studies before releasing land parcels. The development stages are described below and shown in Figure 8.5.

Case studies and examples Figure 7.3 – Global cities’ potential for homes over rail (10km radius)

Figure 8.5 Development stages

Procurement The procurement strategy is driven by five factors: • • • • •

The extent of rail interface (specialist skills) The in-house skills of the developer The delivery model The extent of offsite construction Public sector tendering requirements (where applicable)

The procurement approach may be split into design and construction stages, with the construction strategy related to individual work packages.


Design procurement The successful design delivery will require skills in both the oversite development sector and in rail processes. Three options are available: 1. 2. 3.

Commission consultants with both rail and development expertise - a one-stop shop Commission an independent rail interface specialist to assist the team Employ in-house rail specialists

Option 3 will only be available to larger developers and such skills are unlikely to be currently widely available to the numbers of developers that asset owners are seeking to attract. Options 1 and 2 are therefore most likely and in both, the design team capability should mirror the rail design team disciplines.

Table 8.6 Design matrix Note: Signalling, track & rolling stock covered by asset owner

Construction procurement Works package split The approach to construction procurement reflects the development zones: 1. 2. 3. 4.

The transport system, including tracks, signalling, power The encapsulation, including the new structure constructed over and around the transport system The transfer deck The superstructure

It is assumed in all models that works to the transport system are carried out by the asset owner via one of their framework contractors, with costs reimbursable by the development agreement. The remaining works are assumed to be tendered by the developer/JV vehicle. The encapsulation will need to be carried out by a rail approved contractor, but remaining works may be carried out by a non-approved contractor, as long as the asset owner’s procedures for working close to the railway are followed. This then presents two options; either tender to a single contractor with rail experience, or split the construction into a rail works package and superstructure package. The former delivery route was adopted by both Solum at Twickenham and by Argent at Kings Cross for the Gas Works project. The later model by IJM land for Royal Mint Gardens at Tower Bridge.



Procurement Split 1

3 By Asset owner

The transport system: tracks, signalling, power The encapsulation; New structure constructed over and around the transport system to support


Rail approved contractor

Rail approved contractor

Rail approved contractor

The transfer deck

Rail approved contractor

Approve structural subcontractor

Approve structural subcontractor

The superstructure

Rail approved contractor

Building contractor




• Single point responsibility • Limited supply chain • Programme • Limits funding

• Widens supply chain • Reduces risk through programme • Increased interfaces • Multiple responsibilities

• Accommodates MMC • Increased interfaces • Multiple responsibilities

Figure 8.7 Procurement options

Whilst option 1 keeps all the risk in one place, it may affect the delivery program as the design must be fully advanced prior to tender. It is likely that the works to the asset are carried out during possessions, which will drive the construction program. This option may also make standard funding more difficult to obtain, as residential funders may not be familiar with rail work. It is also suggested that design approval form 1 is in place prior to tender to reduce contractor’s risk.

Procuring offsite The transfer deck The transfer deck is ideally suited to the offsite sector. Suppliers of large pre-cast concrete or fabricated steel components along with on-site specialist assemblers of these components and specialist project management teams are experienced in supplying bridging structures The superstructure The use of offsite is prevalent in the airport and rail industries. However, the residential suppliers may not have experience in the rail sector. Adopting a package construction management (CM) or main contractor approach for the superstructure, rather than appointing them as a main contractor, would allow the advantages of offsite to be delivered. The successful adoption of offsite requires a DfMA approach to ensure that the design is compatible with offsite characteristics and that logistics have been considered. The adoption of offsite should therefore be considered early in the design process.


Figure 8.8 Offsite design considerations

Form of contract It is assumed that the rail works are split into a separate contract. Two scenarios then exist: split packages or a single package, reflecting options 1 to 3 above. Rail works contract These works will be carried within Network Rail or Transport for London’s frameworks to their standard forms of contract, likely to be NEC. Option 1 single contract In this option the entire development contract is let as a single package. One big difference between the 1980s projects and current projects is that the earlier projects were generally procured traditionally rather than through D&B. This transfers significant risk to the contractor. To overcome this a PCSA period is recommended to allow sub-contractors to be engaged, design for construction and obtain approvals. To reduce risk to the contractor it is normal to ensure that all the permanent design approvals are in place prior to contract. The temporary works and method statements can then be prepared during a PCSA period to reduce risk. This option may however may not be allowable under Public Sector Tendering.


Options 2 & 3: Split packages The works may also be split into packages. This would require management input, either in the form of a Project Manager or Construction Manager. The three remaining packages can be split, or combined into a single Design and Build (D&B) package. Encapsulation works The work will involve specialist designs for piling and roof. The permanent works designers will need to specify loads for the foundation and sub-structures. The package is therefore likely to be JCT form with contractor design packages. Transfer deck Similarly, the deck will ned to be detailed to loads supplied by the permanent works designers. If a standalone contract, it is therefore also likely to be a JCT form with contractor design. The superstructure Following execution of the transfer deck the remaining superstructure could be delivered as a single JCT Design & Build contract or alternatively a series of JCT Design and Build Packages under a CM. Both options would allow incorporation of offsite methods.

Public sector procurement restrictions If the client is a public body, such as a Local Authority, then Public Sector Tendering rules will apply. These will mitigate against two stage D&B with an extended PCSA period. Option 2 may therefore be the procurement route. This is likely to require the designers to have obtained the design approvals prior to contract.

References 1. 2. 3. 4. 5. 6.

Transport for London Business Plan 2019/20 to 2023/24, Transport for London, December 2018 Development: Open for Business’, Network Rail Property, Sept 2017 The Hansford Review ‘Unlocking rail investment – building confidence, reducing costs’, Peter Hansford FREng, June 2017 ‘Out of Thin Air: Building above London’s rail lines’, WSP, November 2017 ‘Out of Thin Air: One Year On’, WSP, November 2018 ‘Unlocking land for homes London’ Network Rail Property, September 2017

7. 8.

Asset Protection Agreement; Network Rail. September 2019 Detailed Default Risk Allocation in the Asset Protection Agreement, Network Rail, (undated)


Risk management

General approach

9 1

Given the complexities and risks associated with overbuild, a structured approach is required to sequentially assess feasibility, value and risk. It is fundamental that a risk management system is put in place. This needs to identify the stakeholders and their priorities and be compatible with the asset owner’s own procedures. In terms of de-risking, TFL and Network Rail have established procedures for constructing over and around the railway. Following these procedures goes a long way to mitigating the operational risks. The objectives can then be categorised by stakeholder. It is assumed that the project is Third Party rather than Outside Party in the stakeholder model. The risks can then be assessed by project stage.

Figure 9.1 Stakeholder diagram Given the seriousness of adverse outcomes, the over-riding principles of over-site development are to: • • • •

To avoid risk where possible Allocate risk to those best matched to carrying it Design out risk through project controls Insure for unforeseen risks

Lead Author Patrick Hayes, Meinhardt


1. Avoid risk (consequences)

1. Allocate risk to those who can carry it (responsibility)

1. Design out Risk (project controls)

1. Insure for unforseen risk (insurances) Figure 9.2 Risk management hierarchy

Risk avoidance Network Rail naturally assumes a high premium in pricing risk. It is assumed therefore that the initial filtering process has removed those sites that would pose too high a risk to be financially viable. In addition it is assumed that high value, but complex one-off schemes, such as over-station development are considered on a case-by-case basis and are outside the scope of this report. The guide is predicated on sites with risks manageable through steps 2-4. Further offsite construction has a vital role to pay in risk management. Standard solutions may be tested by initial rigorous modelling and proved in practice, both speeding up project controls and reducing insurance requirements.

Risk allocation A general principle of good project risk management is to have the organisation most capable of managing a risk responsible for doing so. As stated in The Hansford Review3: “Risks are best transferred to those most able to manage and price them… The capacity of private sector balance sheets to absorb risk inevitably places limits on alternative delivery models…. The primary purpose of risk transfer in project delivery is to create incentives for their better management not to find a sink to park risks.” Often in construction, risk management is pushed down the supply chain in ways that give a misguided sense of mitigation. Where operational infrastructure systems are concerned and project complexity is high, the ultimate stakeholder is the owner/operator of the system. They also tend to be well informed with respect to the technical and performance requirement aspects of the system they operate. They are therefore well placed to manage some of the risks of overbuild projects.


Network Rail’s approach to risk This is set down in its Asset Protection Agreement, APA7. The principles behind this are set out in “Detailed Default Risk Allocation in the Asset Protection Agreement” 8 Network Rail undertakes “asset protection” to address safety and operational risks to the railway from the works. The “Third Party Asset Protection Agreement” (APA) (Ref 7) reflects the risk allocation approved by the Office of Rail and Road (ORR) as a “fair balance of risk between Network Rail and investors”, when Third Parties undertake works on the railway. The following high-level principles have been used to underpin and determine the financial allocation of risk within the Template Agreements: •

• •

• •

Network Rail are not funded to assume liabilities from risks arising from overbuild projects. The ORR therefore approved the establishment of Risk Funds to enable Network Rail to assume liability within Network Rail’s liability cap the customer pays into the fund proportionate to the project cost. the Customer funds the direct incremental costs of the scheme, including non-Rail Industry Risk, generally on an emerging cost basis, but a fixed price arrangement may be considered when concluding an Implementation Agreement; where the Customer is responsible for delivery, an Asset Protection Agreement is used and the Customer should transfer design construction risks to its Contractors, or should manage those risks itself where it cannot transfer them; where Network Rail is delivering under a Development Services Agreement or an Implementation Agreement, it will assume risks in the contracts with its own Contractors, up to an agreed capped level; the Customer’s liability to Network Rail for non-rail industry risks may be capped at an appropriate level (although liability for payment obligations, death and personal injury, negligence and fraud is uncapped);


The following table suggests where some major risks associated with overbuild may best be managed, in line with Reference 8. Financial 23 N

Uncertainty for infrastructure owner(s)


Risk under-writing by Government departments (for example, DfT, Treasury, ORR Fund).

21 N

Uncertainty for potential developers


Enabling works create a low risk site.

Interference with infrastructure operations 6 S

Operational systems being affected (for example, the need to reposition them)


Integrate into maintenance program.

21 N

Grey assets issues (old, not compliant with current standards)


Use overbuild opportunity to address the issue. Contribution from asset owner if replacement planned.

36 (carried by party responsible)

Non-availability of operational assets (for example, after a possession for works)

Infrastructure owner

36 S

During enabling works

Infrastructure owner / maintenance contractor / systems supplier

Pre-planning sequence and logistics in detail.

36 S

During containment foundations and box construction

Infrastructure owner / contractor

Procedures and permit systems for working adjacent to and above infrastructure.

36 S

During superstructure construction

Developer / contractor

Procedures and permit systems for working adjacent to and above infrastructure.

Utilities to exploit site (for example, water, drainage and electricity)

Developer / utility companies

Site surveys, above and below ground. Pre-planning.

12 S

Large equipment (for example, for lifting, pumping etc.)

Developer / early stage construction advisor

Consult potential supply chains on needs, availability and access requirements.

12 S

Large components (for example, beams etc.)

Developer/ early stage construction advisor (possibly from component manufacturers or installers)

Consult potential supply chains on needs, availability and access requirements.


Include construction of containment box in enabling works and through procedures and permit systems for working adjacent to and above infrastructure.


Quality management processes applied to safety procedures.


Adopt an offsite, modular strategy.


Select offsite modular system that reduces working at height and the need for scaffolding or other temporary works.


Condition stating that hot works shall not be permitted. Unplanned exceptions requiring a permit.

Access for: 16 S

12 S

Components or tools falling onto infrastructure

12 S 12 S

Working at height

12 S 12 S

Figure 9.3 Risk allocation

Hot works


Key: N: Network Rail Fee Fund provides liability cover in the event of breach of the relevant enhancement agreement by Network Rail. S: Sponsoring Customer (third party promoter) risk, directly or indirectly via the sponsor Customer’s enhancement contractor. C: Enhancement Contractor (from NR). I: Industry Risk Fund. *Cost recovered is passed to customer. The use of financial penalties to mitigate over-runs of possessions should be considered in the wider context.

Risk management Network Rail seeks to manage risk through a Gateway Submission system. TFL operates a similar approach. Both systems follow a similar process of assessment and sign-off covering: • • • • • • •

Asset assessment (and therefore suitability for adaption) Design and construction principals (AIP) Permanent works designs Temporary works designs Construction methodology and scenario analysis Monitoring Long term asset maintenance

Asset assessment Both Network Rail and TFL have standard assessment methodologies for assets, covering condition and capacity. The developer will generally assume costs for amendments to assets required for development. A question remains, however, on how best to deal with assets that are found to be operational but not meeting preferred criteria; “Grey Assets”. These represent an unquantifiable risk and may therefore prevent development.

Design and construction approvals The three approval routes for Approval In Principal, Detail Design and Construction are summarised below. These gateways cover the project technical feasibility, detail design, temporary works design and construction methodology.


Risk reduction through design Risk will predominantly be managed through good design, based around safe construction practices. The design should adopt “Design for Manufacture and Assembly” principles. • •

A constraints plan should be developed prior to the masterplan, which drives the development options. The encapsulation should be as compact as possible with walls constructed inside the rail impact zone. In a rail overbuild, the oversite development straddles the railway corridor. The reinforced concrete rail box allows the railway to function and maximises the development space above. The compact, short-span beams ensure deck costs are in better proportion to the overall development value. Ȉ Ȉ Ȉ


• • • • •

Side walls of solid concrete are preferred to individual columns to deal with impact loads. Total enclosure provides improved acoustic isolation and better contains potential rail impact events. Deck (horizontal structure) should be reinforced concrete to help address fire, robustness and maintenance issues. The technical performance properties of reinforced concrete are well documented, but the material also offers opportunities for offsite manufacture, which could bring significant savings in time, cost and buildability. The deck should be designed as a safety deck, with sufficient coverage and strength to prevent elements falling onto the track.

Vibration control should be addressed outside the rail enclosure and not as part of the base rail works. Measures to isolate noise and vibration are not part of the rail box construction (the realm of the rail authority) but part of the developer’s overbuild design. Resolving such issues can be achieved satisfactorily using tried and tested materials and construction techniques. The superstructure should adopt offsite techniques to minimise program. The building should be built to contain falling objects and/or prevent them falling onto the line. Cladding should panelised and ideally fixed from the inside. Cladding should not interfere with signals, through coloration or reflection. Landscaping should prevent leaves falling onto the line.


Construction methodology, scenario analysis and monitoring Construction risk is controlled by review and assessment of RAMS (Risk Assessment and Method Statements). The works are separated into those that may affect the railway encapsulation box and those that may not. Works within the encapsulation need to be carried out by a rail approved contractor (Achilles or similar). An encapsulation structure then physically separates the works. Where physical separation is not possible, then operational separation by working in engineering hours or possessions is required. Possessions can be very expensive and need extensive notice, so are generally limited to where absolutely necessary. As well as careful planning and control, scenario analysis should be carried out to allow contingency planning. At least three months prior to construction monitoring should begin. Should movements exceed targets, an Action Plan should be in place.

Figure 9.4 Construction risk management approach

Post construction asset management Post construction risk management regarding protecting structures for developers and their funders and the asset owners needs to be considered. The design should demonstrate that the development won’t collapse on the railway in the event of an incident and can be maintained and demolished. Similarly, the design must show that the development remains stable should the supporting structure be damaged. This creates a legal requirement for both parties to maintain their structures. In the event of JV and partnership, this is controlled by the JV agreement. In lease developments, the lease will need to impose duties on each party.

Insurance Public liability insurance Both Network Rail and TFL tend to require substantial levels of public liability insurance as part of their development agreements. This is typically ÂŁ155m, which reflects the maximum level of PLI available on the market. However, this insurance tends not to cover disruption. Liquidated Damages (LDs) for disruption to services will generally be very high. Risk therefore tends to be managed rather than insured against.

Non-damage insurance Non-damage insurance is intended to protect against loss suffered by the developer where there turns out to be no actual physical damage to the railway infrastructure. In these circumstances most conventional insurance policies will not respond but this non-damage cover is intended to cover pure financial losses, such as the amounts paid out by the developer to the railway company under the indemnities in the relevant asset protection arrangement in respect of Network Code payments to train operators.

All risks insurance All risks insurance up to the project value is required by the Asset Protection Agreement.


Assurance As part of their Asset Protection arrangements, both Network Rail and TFL normally require a bond. Where the developer does not meet a prescribed net assets test, they will typically be asked to provide the railway company with an “on demand” bond from a bank in an agreed multi-million pound amount to provide comfort to the railway company that the developer will be able to meet its liabilities. Such bonds do not require proof of loss before they can be called and there will usually be a negotiation with the railway company to agree when the bond should expire. To mitigate the effects of any call on the developer’s bond in relation to defective design or construction, most developers will ask (and pay for) their main contractor to provide them with a performance bond. In contrast to the developer’s bond, performance bonds require proof of breach and quantification of loss before the bondsman is required to pay out and litigation is often necessary, so it will not always be possible for the developer to recover amounts paid out to the railway company from the main contractor.

Figure 9.5 Project risk profile

References 1. Transport for London Business Plan 2019/20 to 2023/24, Transport for London, December 2018 2. Development: Open for Business, Network Rail Property, Sept 2017 3. The Hansford Review Unlocking rail investment – building confidence, reducing costs, Peter Hansford FREng, June 2017 4. Out of Thin Air Building above London’s rail lines, WSP, November 2017 5. Out of Thin Air One Year On, WSP, November 2018 6. Unlocking land for homes London” Network Rail Property, September 2017 7. Asset Protection Agreement; Network Rail. September 2019 8. Detailed Default Risk Allocation in the Asset Protection Agreement, Network Rail, (undated)


Overbuild project management


Challenges facing overbuild projects A rail oversite development project will inevitably be perceived as high-risk and difficult to deliver, resulting in low market interest among contractors for this type of project. Increased cost will be incurred in the design due to the time taken to produce the level of detail required to obtain the necessary approvals, and then in justifying the design during the scrutiny of the approval process. Further cost will be added through the construction stage with works taking place in proximity to the operational railway. This requires restrictions and precautions that are additional to the norm to be implemented as part of the working methodology. These additional costs will challenge the viability of the project, which can be partially offset through increasing the density of development and/or undertaking an oversite development in areas of higher market value.

Early contractor engagement To address the perception of risk and low market appetite, early contractor engagement is essential, so that the perceived risks can be fully understood and mitigation developed. The appointment of the delivery contractor (potentially on a turn key appointment or via a pre-construction service agreement) at an early stage in the design cycle - RIBA stage 3 - is recommended. This will enable the contractor to input into the design so that solutions are developed which support the contractor’s construction method. For example, designing standardised components of a size and weight that can easily be lifted into position during the short windows of access to the railway that are available. Furthermore, through involving the contractor in the design process as it passes through the GRIP (Network Rail project management process) approval stages, the contractor is able to forward plan their supply chain procurement and delivery strategy, having understood the requirements of the railway. Appropriate subcontractors and systems of delivery can be identified, sourced and engaged at an early stage, enabling the works to be priced with greater accuracy rather than speculatively, in order to support the viability of the project. Finally, early contractor engagement also enables the contractor to familiarise themselves with the particulars of the site, specifically the railway infrastructure. As a result, they may develop strategies to minimise any potential operational implications the project may cause. For example the proximity of railway sensitive equipment and its condition, informing the need to change the intended construction methodology or if necessary to protect/divert/ relocate the infrastructure. Surveys of the site can be undertaken and a constraints analysis produced, which also informs the design strategies to overcome these. The opportunities of the site can also be assessed again, enabling the contractor to forward plan the construction method and logistics for undertaking the works on sites which will generally be difficult to access due to the proximity of the railway, therefore facing a number of constraints and restrictions.

Lead Author Daniel Richards, MACE


A collaborative approach Adopting a collaborative approach with Network Rail, and its Asset Protection team in particular, is essential if the project is to be a success. From the outset, a mutual appreciation between parties for both the requirements of the railway along with those of the developer must be formed to underpin the design and delivery stages going forward. These types of projects progress through a combination of more traditional (RIBA) design stages along with the rail (GRIP) approvals process, which don’t always align. Through joint working during the design stages, solutions, which meet the technical requirements of Network Rail whilst supporting the viability of the project, can be developed and incorporated. The asset management team should also be engaged and consulted early so the requirements for the rail infrastructure can be understood and incorporated within the technical submissions. This negates the risk of the design approvals not progressing as planned and becoming prolonged. This collaborative approach is then carried forward to the delivery phase, with the construction methodology jointly scrutinised and agreed by workshopping the proposals so that these are developed in a way to protect the railway, whilst still ensuring efficient construction methodology is followed.

Effective planning of possessions Access to the railway to construct the works will be required out of hours (night works) as well as disruptive possessions to deliver an oversite development. Network Rail’s support in granting possessions of adequate time and spacing will be essential to ensure the contractor can develop an efficient and viable delivery programme. Again, due to the advanced period required to book these possessions (circa six months or more), early contractor engagement is required so that this pattern of possessions can be identified and agreed with Network Rail and other stakeholders, prior to commencement. Due to the required attributes, skills and behaviours of consultants and contractors engaged in oversite projects, it is important to continuously plan ahead. Once set these access dates to the railway are immovable and so progressing the design (to feed the Network Rail approval process) along with the works themselves, so that these intermittent milestones are achieved, is imperative. Time is a substantial constraint with limited scope for late changes or for approvals to become prolonged. It is advisable to set a plan and stick to it. Leadership is required to drive the project forward whilst all parties must buy into this and work together so that these milestones are achieved. That said - as with all construction projects - the unforeseen may occur and on these occasions, collaboration and pragmatism by all parties to overcome emerging issues is required to keep the project on track. Inevitably, prior experience of working on railway related projects is of benefit. Familiarity with the processes and procedures through which the project must accord will assist, although challenging the norms and proposing innovation in the design and construction is encouraged in order to remove complexity and risk, improving overall project viability.


Case Study: Twickenham Station oversite development Developer: Solum Project Manager: MACE Group Ltd Main Contractor: Geoffrey Osborne Ltd Podium sub-contractor: Oliver Connell & Son Ltd Precast concrete sub-contractor: Banagher Precast Concrete MACE was engaged by developer Solum, a joint venture between Kier Property and Network Rail, as project manager for the oversite development at Twickenham Station in 2015. The project oversite development is to be completed in the Spring of 2020 (overall completion by the end 2020). The project comprised the demolition of the existing station and over bridge, diversion of railway operational infrastructure, delivery of a temporary station, and then construction of a development podium over the railway tracks upon which the new permanent station has been built. The development incorporates three blocks consisting of 115 residential apartments, new retail units and public realm. Podium scope: Diversion of railway infrastructure so as not to clash with the podium structure. The podium itself was constructed utilising precast columns and deck beams installed during line blocks and night possessions. The deck was assembled within a single 52-hour disruptive possession.

Figure 10.1 Photo of the podium at the end of 52-hour possession Image courtesy of Solum


Figure 10.2 Image of the development at completion Image courtesy of Solum

Innovation: Taller pile caps were utilised to provide a derailment structure to protect the podium columns; scaffold and net system developed with methodology that allows the scaffold (on the podium over the railway) to be erected during operational hours, saving time and reducing costs (see chapter 5 for further information). Opportunities to exploit offsite construction in the above rail super-structure were limited due to what had been approved at the planning stage. Consideration of offsite solutions should be considered prior to this. They are being used in the final phase adjacent to the line. Project value: ÂŁ62m Commencement on site: March 2017 Forecast completion: Spring 2020 for the oversite development and end of 2020 for the project. Total number of possessions used: 18, of which 6 were for the podium construction.


Conclusions This guide has attempted to capture a range of issues and ideas around increasing overbuild activity and how offsite technologies can be applied. Although there is considerable reference to building homes, there is no reason why the land released cannot be used for mixed developments and other amenities. These other building or landscape typologies are equally suited to offsite methods and systems. Chapter 1 explained the background to much of the thinking in terms of planning and increasing city density. The value of homes close to public transport systems is an obvious benefit alongside the idea of joining the city up where the railway created separation and disconnection. Overbuild should therefore be considered a contributor to new neighbourhoods and linear building typologies alongside and over transport infrastructure. Chapter 2 tackles the subject of how to encapsulate the transport infrastructure. The recommendation is to use robust concrete walls constructed close (in the case of rail) to the track whilst train operations continue. A deck or raft in precast concrete can then be lifted into place whilst train activity is paused. The use of steelwork for the beams would only be encouraged where spans are long. In this way maintenance is reduced and safe operation of the railway or road can be assured. Numerous opportunities for prefabrication and offsite manufacture are discussed, together with the load reduction associated with this approach. Chapter 3 shows how modular and offsite manufactured homes could be deployed over the encapsulated corridor. A variety of configurations of homes is indicated whilst acknowledging planning and other stakeholder impacts of such developments. The value of public realm and desirability of reconnected communities is described and illustrated. Chapter 4 discusses costs for the encapsulation as well as the potential overbuild development. It is certainly the case that carrying out construction activities in the rail environment attracts a cost and programme premium. However if there is a reasonable quantum of development and crucially in a relatively high value location there is likely to be a commercially viable opportunity. The chapter contains guidance on costs per m2 of encapsulation that could be used for feasibility or concept development studies. The cost of land and air rights payments are also mentioned because these have significant impacts on viability. Chapter 5 describes a variety of innovations that could be developed and adopted in the overbuild market. The range of ideas is considerable and provides food for thought in this special type of development. Ideas that give confidence to the key transport stakeholders, enable continuity of safe operations, reduce embedded carbon and maintenance costs, improve stations or passenger experience and attract more people onto the transport network are fundamental benefits. If these benefits can be aligned with new homes and communities then true social value can also be delivered. Chapter 6 describes how the creation of homes and communities supported on efficiently designed decking and encapsulation can provide valuable social, environmental and economic outcomes. Various aspects of these critical ingredients are examined and shown to be particularly positive in the context of overbuild and especially where offsite methods can be adopted to enhance long term sustainability. Chapter 7 underlines the mounting evidence that overbuilding linear infrastructure is taking place at a global level. Many mature and successful major cities around the world see overbuild as a route to the ‘creation’ of land for homes, connectivity and densification generally. These objectives are closely aligned to other city strategies, including reduced car use, improving air quality, wellbeing and investment in public transport networks. Chapter 8 describes how the transport stakeholders have developed asset protection strategies that are flexible enough to enable overbuild work to take place. It remains the case that stakeholder approvals in the procurement process can take time. There are many benefits to be had if excellent communication and collaboration takes place so that confidence in delivery can be assured at every step of the journey. Chapter 9 builds on the procurement topic within the previous chapter and considers the risks associated with overbuild. The methods outlined show that overbuild risks can be identified and managed. The forms of construction, frequently in the live rail or road environment, are not dissimilar to many other types of construction activity undertaken by transport stakeholders. The unique combination of property positioned over the infrastructure corridor provides a challenge, but one that can be addressed within the usual risk management framework. Chapter 10 takes points in the two previous chapters and explains how construction procurement and risk considerations were assimilated into a successful project. The project manager describes how collaboration, innovation, creativity and problem solving all contributed to satisfying the overbuild residential developer, as well as the transport stakeholders. The project is especially challenging because it delivers a new rail station as well as homes over and adjacent to the track. In summary, the conclusions of the initial chapters are that overbuilding is desirable, achievable and sustainable in planning and design terms, especially in conjunction with offsite approaches. The last three chapters demonstrate that by adopting particular management systems and construction techniques with appropriate expertise, it is possible to mitigate risk and satisfy the transport stakeholders in regard to safety and operational continuity.


Afterword This guide leads us to a number of opportunities, some of which challenge the way we do things. Overbuild developments may bring a range of benefits, only some of which accrue to the landowner, developer or future occupants. These include: • • • •

Increasing the value of adjacent areas as a result of high quality overbuild. Reducing the need for individual car ownership thanks to proximity to transport hubs. Increasing property tax yields for local authorities through development of unoccupied spaces. Providing new, improved station facilities, as demonstrated by the Twickenham Station case study.

Where these (and other similar benefits) will accrue to society as a whole, it could be argued that government, both central and local, should look to enable such projects, and so it is worth considering how this could happen. Ideas that have arisen during the creation of this guide include: • • • •

Treasury releasing funds for the creation of developable sites (the supporting platform or box). The cost of capital reflecting a government’s true cost of borrowing (rather than private sector commercial rates that provide for both shareholder and corporate bond holder returns). Planning authorities considering relaxing the height limitations at or close to transport hubs to enable 12 storeys or more for appropriate central locations. Landowners, for example rail and highways networks, de-risking such projects with respect to the operational infrastructure below them. This could be by managing and constructing the civil engineering works prior to formal developer involvement. Using or development of a more collaborative approach to contracting, where risk really is managed by the organisation most capable of doing so.

Associated civil engineering structures do need to provide very long term, low maintenance infrastructure encapsulation for all that is constructed above. Repairs and deterioration within the operational zones should be avoided wherever possible and whole life cost of the works optimised. If a true cost of capital for public sector works were to be used for the civil engineering package, a more realistic whole life cost analysis would result, as future costs and benefits would not be discounted out of the equation. Structural healthcare that is being retrofitted to structures could be incorporated from the design stage. The need for our cities to grow will continue to require the release of land for, in particular, residential development. Overbuild enables us to re-use land that was cut out of our communities, particularly in the Victorian era of railway building. We now have an opportunity and a need to reverse some of this and offsite construction can help maximise this opportunity.