Gillard Associates Ltd
De Carbonising Welsh Housing: Borfa Place, Blackwood
Outline Proposals Constructive Thinking Ltd April 2020
Outline Proposals
1 Introduction This report is a response to an invitation from Mi-Space to be included in a framework agreement for the de carbonisation of Welsh social housing, as a response to 'Better Homes, Better Wales, Better World' published in 2019. This nationally important initiative is intended to address the following key issues: ● reducing the carbon footprints of existing housing stock to help government meet national policy commitments for combatting climate change ● reducing the problem of fuel poverty in social housing This particular appointment relates to the Borfa Place estate in Blackwood, a small development of 20 dwellings built around 1994. The report aims to provide a solution to the problem of how to make energy efficient an estate of houses which were constructed at a time when Building Regulations were much less stringent. The proposed solution needs to satisfy the following criteria: ● deliver an improved energy performance for each dwelling sufficient to satisfy WG benchmark ● be simple, practical and achievable ● be cost effective ● disrupt the lives of the occupants as little as possible and for as short a time period as practical to achieve the desired improvements
Gillard Associates Ltd is an architectural practice based in Cardiff and has been recognised for its work in sustainable housing and community projects. The founder of the practice Alan Gillard has been at the forefront of sustainable design since inception, and this is reinforced by hands on practical knowledge and an understanding of building science gained threough post graduate study. The firm developed the LivEco concept for housing: the award winning Great House Farm eco village is an exemplar project which confirms that joined up thinking in the planning, detailing and construction of new homes is achievable and provides not only truly carbon neutral living but helps to establish cohesive communities and improve the quality of life for its occupants. The key concepts employed are: - PassivHaus principles of fabric first construction - Air tight interiors and positive pressure ventilation /MVHR - Sustainable heat production - Passive cooling - Extensive use of local supply chain for components and materials - Energy storage and renewable energy generation - Co housing features to promote community cohesion Alan welcomes the idea that, with this new initiative from MiSpace, these principles may now be applied to the existing housing stock.
The benchmark has been identified by Welsh Government as SAP92A. In other words, to exceed current building regulation compliance under Approved Document L1A (SAP 74C) This report has been compiled by two architectural practices well known for their work in sustainability and energy efficient housing - who have collaborated together for well over ten years.
GILLARD ASSOCIATES architecture and design
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Constructive Thinking Studio was founded in 2002 by Jon and Hannah Moorhouse and is based in Liverpool. The studio has a fully established reputation especially in the fields of Sustainable Architecture, Housing, Retrofit, and Building Information Modelling (BIM). The studio is constantly evolving, and encourages each of team members to explore and test new ideas. Our collaborative design process is the basis of everything we do which is underpinned by a wide range of research in both professional and academic fields. All of our projects are modelled digitally in 3D allowing for seamless co-ordinatation with other consultants, optimising all of information prior to work commencing on site, with continuous improvement across all projects ensuring every client benefits from our best work, at all time. We are able to test our models for energy efficiency and our details for thermal performance early in the design stages. Running costs can be significantly more than the capital cost of any project, so our ability to test any proposals as we work is proving invaluable to our client base. This design development allows us to work thoroughly through established stages of the RIBA plan of work, and be effective in resolving solutions for wide range of projects. Communication and collaboration among colleagues and other professionals is key to the success of every project, and we ensure this is achieved throughout every stage of all projects, however large or small.
Decarbonising Borfa Place Blackwood
2 Methodology 2.1 Survey
2.2 Computer Modelling
2.3 Retrofit Recipe
The proposed retro fitting solution methodology needs to be practical yet flexible: a 'one size fits all' approach is unlikely to be successful, since dwellings come in many forms, in different locations, and with sometimes conflicting priorities, eg, houses in conservation areas where aesthetic concerns may outweigh the need for energy efficiency.
Once the survey has been translated into a BIM model the project will invariably proceed as follows.
Balancing the available budget and achieving energy efficiency in the virtual dwelling is achieved by putting together a combination of retro fit technologies, as listed below. With experience it is possible to get a feel for the combination of measures needed to achieve the optimum outcome. Obviously the more modern the dwelling, the less onerous the interventions need to be. For a low rise dwelling the 'recipe' usually includes a combination of all or some of the following:
The solution must be appropriate to the building typology, which is to a greater extent, influenced by the period of construction. It must therefore be based on a sound understanding of the existing construction, and its capability to support retrofitted materials and components. SInce the proposed solution is based on a 'desk top' study certain assumptions have had to be made in the preparation of this report. If the project were live then a detailed survey of at least one dwelling would be made to ensure that the original construction techniques employed are recorded and understood. Also, as the proposed retrofit solutions (see next section) are to be prefabricated for speed of installation on site, it is essential to make sure that all structural openings, service positions, projections and the like are recorded accurately. Cloud based survey techniques would be employed to allow the designers to accurately model the building and co ordinate the applied finishes with the supply chain.
Example of point cloud survey
Using Graphisoft Archicad the buildings are modelled precisely. This enable the designer to quantify the existing building and using the built in thermal modelling engine obtain a theoretical performance based on typical occupancy. At the same time the data can be exported to a SAP calculator so that the current rating can be checked, but more importantly, to provide a base model which can be compared with subsequent iterations of the model as energy efficiency measures are proposed and 'tested'. The model can be viewed at important stages so that the effects of various interventions can be understood. Quantities can be extracted so that construction budgets can be allocated. In the case of prefabricated building elements like cladding and windows, the model can be used to co ordinate procurement.
● External wall insulation ● Additional roof insulation (either interstitial or over roofing) ● Perimeter insulation below dpc (since increasing the amount of floor insulation is usually not practicable) ● Replacement windows and external doors with emphasis on air tightness at reveals and opening sashes/leafs ● Installation of mechanical ventilation with heat recovery ● Replacement of existing heating boiler to disconnect the dwelling from the gas grid ● Replacement of hot water storage ● Treatment of thermal bridges eg at reveals, heads and cills ● Heating/DHW control simplicity It is important to understand that the recipe works only when installed as a complete package, but also when the occupants are included in the process: human behaviour has a significant effect on the performance of low energy dwellings, and although outside the scope of this report, education or training in the use of the controls and more fundamentally, how the building responds to outside conditions, should be included as part of the package to optimise the investment.
BIM model constructed from point cloud survey
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Outline Proposals
3 Retrofit Technologies 3.1 External Wall Insulation
3.2 Roof Insulation/PV Integration
3.3 Slab Perimeter Insulation
There are many EWI products and processes. Our preferred solution is Mauer UK who manufacture bespoke prefabricated wall panels based on point cloud surveys with a finish that can closely mimic many common facing materials.
It is assumed that the dwelling currently has a traditional ventilated cold roof with insulating quilt at ceiling level. Whilst it is possible to increase this insulation in practice it is difficult and is likely to increase condensation risk due to poor ventilation.
Since insulating the existing ground floor is impractical the easiest method of upgrading this thermal element is to insert perimeter insulation below dpc level. The depth of the insulation should be no less than 600mm, which effectively enables the ground bearing the slab to become a heat store.
Benefits of Mauer UK: ● quick year round installation from mobile scaffolding ● breathable fire resistant insulation in virtually any thickness ● 30 year guarantee and design liability ● replication of surface may obviate the need to obtain planning permission ● full range of accessory elements meaning cills and other fetures can be replicated and the originals left in situ
It is also difficult to remove cold bridging when the EWI does not 'meet' the insulation at eaves level. The best solution is to place the insulation layer outside the roof giving the whole house a warm envelope. Obviously this necessitates the removal of the existing roof covering and its replacement over the insulating layer. Our preferred option for over roofing is an integrated system of roof covering and PV cell installation. GB-Sol have a range of solutions which have been well received. It featured in the Solcer £100k House conceived by Welsh School of Architecture's Phil Jones. In our proposal we have allowed for a 2kW array which can feed into the grid and supplement hot water heating. This could obviously be increased depending on available budget.
Mauer UK Top left: before Bottom left: after Above: cladding detail
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The example below illustrates the concept and the heat losses reduced as a result of the removal of this thermal bridge.
Decarbonising Borfa Place Blackwood
3 Retrofit Technologies cont'd 3.4 High Performance Doors and Windows There are many choices for low energy doors and windows. The key factors influencing choice would be: ● low U-value/well draught sealed ● provenence: select local manufacturers if possible ● materials: timber is a more sustainable material than aluminium but this needs to be balanced against maintenance ● cost ● aesthetics ● security: HA's normally require Secured By Design compliance
3.5 MVHR and Air Tightness
3.6 Air Source Heat Pump
Mechanical ventilation with heat recovery is now becoming standard on low energy housing. MVHR systems work by combining supply and extract in one unit. Moisture-laden, stale air is extracted from ‘wet’ areas, such as kitchens and bathrooms. The heat from this stale air is recovered via a heat exchanger, and this tempered air delivered into the living areas of the home.
Welsh Government is committed to switching housing away from the gas grid.
Retrofitting MVHR units in existing dwellings can be intrusive, as ductwork needs to be taken from the wet rooms back to the unit. If this is a barier to installation then a second best option would be for a positive pressure fan to be installed in the attic but this would compromise the energy efficiency of the dwelling.
Our preferred option is one of the ranges marketed by Green Building Store. They offer a range of different products but all are FSC chain of provenance, low emissivity triple glazed, providing very high energy efficiency.
A prerequisite for installation is the reduction of air leakage from the dwelling. With attention to detail it should be possible to achieve less than 2ac @ 50Pa and this figure is assumed in the SAP calculations.
Note that the usual trickle vents will not be required (see next paragraph) and there needs to be an emphasis on air tight construction and workmanship.
Assuming MVHR can be installed our preferred choice would be by Nuaire, manufactured in S Wales, Nuaire’s MVHR range recovers heat at 95% efficiency, making it the most effective range currently available. In warmer months when cooling is required to maintain comfort levels, Nuaire’s MVHR Eco range offers 100% bypass with no loss of resistance.
Effectively this means that, using currently available technology, heat producing equipment is limited to heat pumps of various kinds: ground source (GSHP), air source (ASHP), or exhaust air (EAHP). EAHPs are useful in small dwellings or flats, where hot water demand is lower. Retrofitting the units can be problematic due to their size and weight, and the amount of work required in connecting pipework and ductwork. GSHPs are relatively expensive due to the need for a borehole: there is unlikely to be sufficient space for a ground loop. A GSHP combined/district heating scheme may be feasible for some projects but for this application we have decided that the connection of an ASHP for each dwelling is the most economical and practical solution. The performance of ASHPs has improved in recent years and inter seasonal CoPs can now be expected to reach around 3.5. We have no preferred choice of unit as it is likely to be based on factors we may not be aware of, eg, maintenance contract, economies of procurement, warranties etc.
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Outline Proposals
3 Retrofit Technologies cont'd 3.7 Insulated HW Cylinder and Radiator Conversion Generally the dwellings' DHW cylinders are undersized and/or under equipped for energy efficient use. Gravity fed hw systems are still common and any upgrade would need to include a mains pressure system. A large heat store will provide better hw reliability as recharge times with ASHPs can be slow compared to a gas boiler. Well insulated jackets are now much better at storing heat. It is also advisable to enable surplus solar energy from PV cells to help heat the hot water which can be controlled by a smart control (see later paragraph). We do not have a preferred choice for the HW cylinder, but the size should be such that the largest practicable solution will fit into the available space.
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3.8 Heat Emitters
3.9 Controls
It is assumed that the existing dwelling heated with high temperature radiators on a circuit connected to a gas boiler.
Experience in new build housing tells us that simple controls are an essential part of the solution. The installation as far as possible needs to be 'fit and forget', in other words, as few interventions by the occupants as possible shoud be required.
The boiler is to be replaced with a ASHP which supplies low temperature hot water for heating. It is anticipated that the greatly reduced heat requirement of the dwelling following improvements will mean that the existing radiator network will be sufficient for space heating. In our proposal no replacement of heat emitters is considered necessary, subject to detailed review.
Generally low energy houses with renewable technologies require some sort of Building Management System (BMS). This can be complex to balance so it is recommended that the dwelling is fitted with a simple thermostat for temperature control, and this is backed up with a cloud based BMS and Smart meter so that the systems can be managed remotely by the HA.
If there is a shortfall in heat output this should be possible to rectify by the installation of larger capacity radiators.
For example, CO2 detectors and humidity sensors linked to the MVHR system can be configured to suit individual circumstances.
Decarbonising Borfa Place Blackwood
4 Proposals 4.1 Summary The cutaway illustration indicates the intended conceptual retrofitting work required. The dwelling type selected for the proposal is the simple semi detached type (house no 1 and 2). Demolition work includes: ● removal of roof tiles, rainwater goods, and all projections such as fascias ● the rafter feet are taken back to existing wall face ● excavation of perimeter footpaths ● removal of windows and external doors and frames ● removal of boiler and flue, HW calorifier
New integrated PV roof system laid on rigid insulation boards As 2.2
New roof oversails wall cladding
Note wall cladding and roof junction: continuity of insulated layer
New high performance triple glazed windows
Whole house ventilation system MVHR
Construction Phase: Mauer EWI is applied to the face of the external walls on its integrated framework. This can be extended vertically to meet the new roof surface position. The roof is over boarded and insulated and fitted with the new roof covering.
New 180l DHW storage
Window replacement follows, together with refitting rainwater goods. Internal Works: Some disruption will be necessary to install the new DHW storage, and connect the F&R from the heat pump. The MVHR unit and associated ductwork/registers will need to be fitted. It is suggested that positioning the unit in the roofspace will minimise the need for builders' work.
● New insulated roof panel
Wall cladding: brick faced offsite manufacture EWI system
High security/ performance doorset
Air source heat pump connected to existing boiler terminals
Below dpc perimeter insulation to improve thermal performance of floor slab
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Decarbonising Borfa Place Blackwood Existing Building
5 Calculations 5.1 Summary The data obtained from the BIM model was fed into the SAP tool (CT are registered SAP assessors). The table right summarises the results in three parts: a) top, the SAP rating of the existing dwelling b) centre shaded pink, the SAP rating of a retrofit designed to meet current building regulations Approved Docuemnt L1B c) bottom shaded green the SAP rating of the proposed retrofit, to meet the benchmark required by WG, ie, SAP 92A. The 'de-carbonised' dwelling should achieve a SAP rating of 94A and annual energy consumption for heating and hot water of around 27 kWh/m2/ain theory should be achievable. For reference PassivHaus standard is 15kWh/m2/a. This SAP rating could be improved by the addition of solar PVs and in theory carbon zero space heating could be achieved. A 4kW array would give a SAP rating of 104A.
5.2 Caveats Limitations and Assumptions Due to restrictions at the time of compiling this report (Covid-19) it was not possible to visit the site to undertake survey work. The report is therefore to be considered a desktop study and interpreted accordingly. The existing methods of construction were deduced from the original plans provided and a working knowledge of standard contemporary building techniques. It is assumed that a level of air tightness can be achieved and this could be verified on site with air pressure testing. This is an aspirational level which is achievable but requires attention to detail and good workmanship. Note that the solution provided is tailored to the semi detached dwellings simple on plan. Staggered footprint dwellings may require a slightly different solution due to additional heat losses through greater external surface area.
Doors Windows Walls Party Wall Cold Roof Warm Roof Floor Thermal Bridging Ventilation Loss TOTAL
W/K 5.67 32.7265 27.7474 19.7 19.8528 0 13.51 72.564 264.0619 455.8326
% Benchmark 1.24% 3 7.18% 2.4368 6.09% 0.34 4.32% 0.50 4.36% 0.47 0.00% 0.00 2.96% 0.32 15.92% 0.40 57.93% 15 @ q50
Description of Measure SAP Default SAP Default Calculated from assumption SAP Default Calculated from assumption Calculated from assumption Calculated from assumption SAP Default SAP Rating 67 D 2 SAP 10 CO2 40.74 CO2/m
Space Heating Demand
Part L1B BAU Retrofit
Fuel Bills W/K
Doors Windows Walls Party Walls Cold Roof Warm Roof Floor Thermal Bridging Ventilation Loss TOTAL
%
3.024 20.1955 24.483 19.7 6.7584 0 13.5168 27.2135 194.3985 309.2897
Change 0.98% 6.53% 7.92% 6.37% 2.19% 0.00% 4.37% 8.80% 62.85%
1.6 1.6 0.3 0 0.16 0 0.32 0.15 7 @ q50
L1B Table 1 L1B Table 1 L1B Table 3 As Existing L1B Table 3 As Existing As Existing SAP Default Minimum New Build Value 74 C SAP Rating 28.44 CO2/m2 SAP 10 CO2
Fuel Bills W/K
%
Change
Doors Windows Walls Party Walls Cold Roof Warm Roof Floor
1.89 11.4165 10.6093 19.7 0.1173 5.4736 11.8272
1.10% 6.64% 6.17% 11.46% 0.07% 3.18% 6.88%
Thermal Bridging Ventilation Loss
16.6493 94.2876
9.68% Calculated 54.83% 2 @ q50
TOTAL
171.9708
2 124.47 kWh/m /a 27.01% Reduction
Description of Measure
Space Heating Demand
Bid Proposal
10452.0861 kWh/a
1 0.88 0.13 0.5 0.23 0.11 0.28
SAP Rating SAP 10 CO2 Space Heating Demand
7131.5043 kWh/a 2 84.93 kWh/m /a 84.98% Reduction Description of Measure New Eco Door Triple Glazing EWI As Existing Porch roof insulation Rafter Level Insulation Perimeter Insulation Themally Optimised Details & MVHR
96 A 4.66 CO2/m2 2267.5266 kWh/a 2 27.00 kWh/m /a
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GILLARD ASSOCIATES architecture and design
Gillard Associates Ltd The Quaypad Cardiff Marina Watkiss Way Cardiff CF11 0SY T: +44 (0) 2920 229 133
Constructive Thinking Studio Ltd Liverpool Science Park 131 Mount Pleasant Liverpool L3 5TF T: +44 (0)151 705 3433