Adaptive Reuse, Issue #2: A Path to Carbon Neutrality

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Eddie Jump, BEng, CEng, FICE Director Eddie’s wide-ranging expertise includes working with clients to find value in complex urban sites in London. His diverse portfolio ranges from the delivery of six-storey extensions atop Grade II listed buildings to schemes for low-embodied-carbon towers, all within the City of London.

+44 7799 765988 EJump@ThorntonTomasetti.com

Duncan Cox Senior Associate Duncan specialises in incorporating sustainability into structural and façade designs. He applies a whole-life carbon approach to each project, reducing both embodied-carbon and operational footprints. Duncan serves on several a number of embodiedcarbon task-force groups.

+44 20 3992 9535 DCox@ThorntonTomasetti.com

ADAPTIVE REUSE

Issue #2:

A Path to Carbon Neutrality As the AEC industry transitions to a low-carbon future, reuse of our existing building stock will be essential in delivering zero-carbon buildings grounded in circulareconomy principles while reducing expenses related to the expected rise in carbon taxes.

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Hobhouse, London, fell below LETI’s proposed 2020 embodiedcarbon targets, even though we

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Policy In accordance with the Paris Agreement, the United Kingdom has set a target of net-zero carbon emissions by 2050. To support this commitment, the country’s government will implement many green laws and regulations in the coming year, covering provisions beyond those of Building Regulations Part L, which have dominated to date.

Recently, we’ve seen a spate of activity from institutions like the U.K. Green Building Council, laying out net-zero frameworks. These are being closely monitored by local authorities looking to update their planning regulations to adopt net-zero targeting.

Reducing Carbon Footprint It is widely recognised that achieving true net-zero carbon will require the adaptation of existing buildings as new-builds with current material technologies and standards fail to meet the required embodied-carbon thresholds.

Every cubic metre of building material has a related carbon footprint – from excavation, manufacture, transportation, construction and waste. The building’s carbon footprint continues through its operation and maintenance and includes end-of-life emissions related to deconstruction, demolition or repurposing.

Each of these stages offers opportunities to reduce the carbon footprint. Repurposing all or part of a building can significantly reduce the volume of material required to deliver a new facility.

Moving to a circular economy structure in which building materials, elements, zones, etc., are repurposed and reused, rather than demolishing and starting from scratch, can yield additional savings. This circular economy model is expected to result in a more sustainable future.

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The Building Industry The building industry has come under increasing pressure from activist groups to move to a net-zero future by 2030. This new approach will offer incentives to retain structures and prevent wasteful demolition and subsequent reconstruction and to measure building whole-life carbon with progressive targets for improvement over time. At the same time, Part L revisions will limit energy use and legislate improvements to external fabric. Buildings will be expected to meet aggressive energy-use intensity (EUI), embodied-carbon and circular-economy targets.

The Greater London Authority (GLA) has already instituted a carbon offset tax that applies to major developments for operational carbon, which is expected to rise to around £100 per tonne of CO2. These types of taxes will extend to a broader range of developments, incorporate embodied as well as operational carbon, and increase over time. Conducting life-cycle assessments (LCAs) and developing repurpose models provide opportunities to minimize the environmental impact of new developments and reduce costs from materials and carbon offsets.

A recent publication from the Royal Institution of Chartered Surveyors suggests that the elements that can be retained on an existing structure (such as superstructure, substructure and external works) represent about 50 percent of a building’s construction cost.

Energy Performance through Façade Replacement Adapting or replacing the building envelope can significantly enhance a building’s performance and impart a modern aesthetic to a reused frame, reducing programme, cost and embodied carbon. New highperformance façade technologies are appearing on the market at a rapid pace. Upgrading the façade by reducing solar gain/loss, improving natural light levels and reducing leakage can substantially reduce the building’s operational energy demands.

Atriums can be adapted to create © Perkins Ea stma n

passively managed spaces that add enormous value in terms of user well-being.

Complementary treatments like integrated photovoltaics can transform façades and roofs from energy impactors to energy providers. Low-rise buildings with efficient systems have the potential to produce enough energy to sustain themselves without using grid-supplied sources.

This can help to realise a net-zero operational energy budget without requiring costly carbon offsets.

Existing arrangements can be adapted to improve the thermal comfort of users. For example, atriums that provide additional “outside” spaces can be created between buildings. These can be carefully designed not only to allow solar heat gain when needed but to benefit from cooling from natural ventilation. Such passive measures produce additional spaces that are effectively cheaper to run and add enormous value, in terms of user well-being.

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Embodied Carbon Manufacture, Transportation & Installation of Construction Materials

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Life-Cycle Assessment (LCA) The life-cycle assessment is an excellent methodology for understanding the carbon footprint 2 of a development and determining where savings can be made by applying different carbon factors to different materials, products or processes. An LCA can help quantify the benefit of repurposing a building to understand the difference in the quantity of material that could be saved compared to building

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new. The life-cycle approach is becoming the norm, and future regulations will require the capture of the environmental impact of all of a building’s life-cycle stages, not just the operational stage.

The GLA plan specifies that LCAs be conducted on all referred projects and recommends that they be performed on all major developments as well.

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372kg CO2/sm of Embodied Carbon

Metric Tonnes CO2e Saved in Slabs & Framing

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Case Study Hobhouse, London Situated adjacent to the National Gallery, Hobhouse is a complex refurbishment and new-building project, which included the retention, restoration and redevelopment of a Grade II listed building designed by renowned architect John Nash and the unique Grade II listed subterranean masonry vaults.

We provided structural and façade engineering services for the refurbishment of one of the listed structures, enabling the Royal Watercolour Society to return to the building where it had been housed for 115 years, from 1823. This refurbishment included the addition of two residential floors at the roof level of the three-storey building.

The remaining 19th-century buildings, which had been unsympathetically redeveloped in the ‘70s and ‘80s, were in poor condition. Their façades didn’t align with the street, their footprints were underutilised and their public spaces were hard to locate.

Demolition of these buildings and construction of a larger openplan frame building provided new retail, office and residential amenities. It also created a newly aligned streetscape and public spaces, offering a more direct pedestrian route across the site and a new entrance to the restored vaults. Retention of the vaults saved considerable construction time, avoiding risk and reducing embodied carbon. The new buildings comprise lightweight, lower-embodiedcarbon materials, resulting in high-performance spaces. The reduced building mass allowed us to build taller, creating additional space.

The design team and client agreed to the goal of developing a low-embodied-carbon building by combining material retention with efficient design. Thornton Tomasetti’s carbon calculator has measured the embodied carbon of the building’s structural elements as 375kgCO2e/sm and the overall building figure at 495kgCO2e/ sm.

The building’s embodied carbon fell below the London Energy Transformation Initiative’s (LETI) proposed 2020 targets, even though we conceived its design much earlier, in 2013.

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