How we measure impact
Why do we measure?
Reducing construction’s negative impact on the environment is a big task, and as designers in one of the most polluting industries we must rise to the challenge. We measure our impact across a range of criteria, informed by our experience, and groups such as the IStructE, RIBA, the UKGBC and LETI. By tracking these values on projects, we seek to continuously improve, to respond to the sustainability aspirations of our clients, and to design first class sustainable buildings we can be proud of. As a research and innovation driven practice this also enables us to lead by example, and to participate in industry wide data gathering and sustainability conversations.
Structural embodied carbon (kgCO2e/m2 GIA)
Embodied carbon measurement puts a number to all the emissions we don’t see in the operation of the building, such as the extraction of raw materials, manufacturing them into final products, and transporting to and from our site. The lower, the better. Tracking and reducing a building’s embodied carbon is essential to reducing our environmental impact, and structures account for a significant proportion of this. We measure embodied carbon at all design stages: early on to inform the best options for the structure, and later to quantify the final environmental impact of the design. Many sustainability initiatives today are centred around reducing embodied carbon to specific targets, so accurate measurement of structural embodied carbon ensures we can support our clients in meeting and exceeding their targets. Where projects involve an element of structural retention (see below), the stated overall structural embodied carbon per m2 factors in the embodied carbon saved by retaining some or all of the existing structure.
Material intensity (kg/m2 GIA)
Material intensity looks at how much material was used in the structure of a building. It is a way to quantify how much new stuff has been used – a measure of circularity, rather than environmental impact. In general, the lower the better, as lower material intensity means less mass of new material was used per m2 of the new building. Effective use of materials leads to efficient structures. By combining material intensity and embodied carbon measurements, we can identify carbon hot spots and optimise our materials choices, and guard against wasteful use of materials that are low in embodied carbon.
Existing structure retained (% volume)
A powerful way to reduce impact is to use less stuff, and one great way to do that is to retain what we already have. Structural retention has been a key feature of many past HTS projects, and we always seek to explore these options first. Retention also preserves character and connects the occupant emotionally with the history of the building. The construction industry often sees buildings as disposable, but challenging this assumption can create buildings which retain their cultural and historical interest, while also being more sustainable.
Steel/concrete reused (tonnes)
Where structural retention is not possible, there is still significant carbon to be saved through reuse of structural concrete and steel. This is a double ended process as we can preserve elements of the existing building for later reuse, and can incorporate reused elements on our new building, or both. Reuse is also about more than carbon – it reduces waste and supports the transition to a greener economy. Today steel reuse is better established than concrete as steel is more modular and workable, however both materials are rarely reused so there is great room for improvement here, and we are exploring this approach on projects and through research.
Carbon emitted vs. carbon stored (kgCO2e)
Reducing carbon emissions is a powerful way to reduce our environmental impact, but some materials go one step further and lock in atmospheric carbon. Trees sequester carbon as they grow, and this carbon is stored in a building made from that timber. Factoring this absorbed carbon directly into our embodied carbon values can be misleading as poor design and materials choices can be cancelled out by using large amounts of timber inefficiently. Instead we consider this stored carbon as a separate quantity to be considered as an additional benefit, and seek to use timber for its wider benefits rather than simply as a carbon offsetting mechanism. Standards around carbon reporting continue to evolve and this approach is aligned with the most recent RICS guidance for whole life carbon.