As part of our Carbon Matters series, we want to share some of our thinking around the reduction of embodied carbon emissions from the buildings we design. We are a reuse practice, with the regeneration of existing buildings central to our ethos. However, new build elements are often required to make existing buildings function now and into the future. Central to our approach of recent years is to interrogate the way we construct our new building elements in detail, avoiding jumping to standard solutions. We look at ways of reducing the quantity of material used while still achieving the same outcome in terms of function, quality, and aesthetic.

The below diagram shows the wall build up of a cultural project we completed five years ago (right), and a similar wall build up of a cultural project we have on the drawing board just now (left). Our thinking has changed and developed to focus more acutely on reducing embodied carbon emissions. Both buildings require 60-minute fire rated external walls. Both buildings have rainscreen cladding systems.

The completed right hand side project is business as usual – steel structural frame with SFS infill, weather defence board, non-combustible mineral wool insulation and cladding externally. However, in this case we had to line the inner face of the SFS with two layers of plasterboard to achieve the 60 minute fire rating. This necessitated a further independent lining stud with plasterboard lining internally to provide a finished wall. The build up contains eight different layers of material. The u-value is only 0.22 W/m2K while the embodied carbon is 235kgCO2e/m2.

The proposed ‘lean’ build up on the left includes a CLT structural wall. The CLT wall has been designed with charring zones to achieve 60-minutes fire rating without further linings or layers. The CLT wall also provides a beautiful internal finish and so eliminates the need for additional internal wall linings. Externally, the weather defence board is omitted as the CLT provides a solid fixing ground for the cladding rails. The external build up of non-combustible mineral wool insulation and cladding remains the same. This ‘lean’ build up contains only five layers of material but achieves a better u-value of 0.15 W/m2K. The embodied carbon emissions of this build up are only 80 kgCO2e/m2.

We believe that careful interrogation of how we build, not just how much we build, will support a lower carbon construction industry.

The embodied carbon emissions were calculated using OneClick LCA software and are accurate to the best of our knowledge using EPD information from actual products used or region specific generic data.