As a sector, we are getting more adept at producing designs and specifications that reduce operational carbon, but there is less clarity on how to reduce the embedded carbon in the projects we deliver. Tom Webster, one of our three industry experts, gives his view as to how this should be addressed.
Bicycle storage facility at the University of Amsterdam designed in the 1960s by Norbert Gawronski and remodelled by AHMM in 2014. Basement space accounts for 10-20 per cent of a building’s embodied carbon, rising to 50-60 per cent when used in conjunction with a low carbon superstructure. Credit: Timothy Soar
Change legislation and policy
It has often been a source of confusion to me that as a structural engineer the type of structures we design are not more regulated in terms of embodied carbon. It consistently falls to either the structural engineer to push for a low-carbon solution or the client/ funder’s ESG programme to set a brief with one of the LETI targets. Sadly, it is not being driven for national or global benefit by our national and local governments.
By contrast, our colleagues in architecture and building services design have had the planning process and Building Regulations impose various constraints and targets on operational carbon and the use of renewable energy, which have provided vast improvements, such as higher performing fabrics and less noise and air pollution.
The cynic in me has always concluded that as most structural construction materials are imported to the UK, their carbon cost is in other countries, and is therefore not seen as our problem at a legislative level: if it doesn’t contribute to our national carbon emission, why should we worry about it? But that’s hardly the attitude to address our growing climate emergency.
Taking responsibility
It is important to acknowledge that some local authorities, such as Westminster City Council, Oxford City Council and the City of London, are now asking for embodied carbon assessments for some schemes going into planning. But it is not clear what targets need to be reached and what concessions will be made to allow these to be met. The new London Plan requires whole lifecycle carbon emissions using both embodied and operationals carbon over the life of a building to be calculated. This is a good start but needs to be backed up by the National Planning Policy Framework and aligned with rigorous targets for the reduction of carbon within buildings.
Given 50 per cent of the embodied carbon of a building is within its structure, it is of importance that it should be baked into both the National Planning Policy Framework and Building Regulations. The construction industry has led on this issue by developing a proposed amendment to the Building Regulations called Part Z. This is a proof of concept for how the measurement and regulation of embodied carbon within buildings could be implemented. There does not seem to be the same desire to push for change in the National Planning Policy Framework and it is being left to individual authorities to decide if and when they want to place targets on embodied carbon.
Planning policy is not simple to navigate. Imposing a LETI 2030 target on embodied carbon may not solve the issue, as often the design process is about striking a balance so the solution meets all policy requirements. Providing large-scale low-embodied carbon buildings may mean that you simply cannot meet other targets and stipulations. But any target would be better than no target, and in the short term, whilst we wait for material innovation and decarbonisation of the energy grid, planners could be empowered to mediate planning policy to ensure policy or legislative requirements are not increasing embodied carbon.
Basements and bicycles
Research by the Institute of Structural Engineers has shown that in typical buildings, 10-20 percent of the embodied carbon of the structure is in the substructure. By far the biggest offenders are buildings with basements. This gets worse when a low carbon superstructure is adopted, as the basements then make up 50-60 per cent of the embodied carbon within the structure. With basement construction, the primary source of embodied carbon is typically in reinforced concrete walls and supporting steel or concrete pile structures, as well as thick basement slabs. The forces involved mean that below-ground structures are much larger and stiffer than above-ground ones, and the nature of these forces and durability requirements preclude the use of carbon efficient materials, such as timber. If we want the construction of lowcarbon buildings to become commonplace, we need to ensure that policy and regulatory requirements enable this. It should be quicker and easier to adapt our regulations and policy than wait for a miracle material to appear.
Clients I speak to are often not very thrilled about building basements as they are expensive, provide poor quality space and tend to contain many of the significant risks in a project. However, they reluctantly build them to create enough net internal space to make the building viable, and to meet other planning requirements. Limits on the height of a building, limits on noise from plant, the number of bicycle storage spaces and showering facilities, and urban greening of roofs are all individually valid, but together create a suite of policies that tend to be negative instead of positive when it comes to embodied carbon.
For instance, the number of cycle spaces required to meet planning regulation always causes me to wince. Before everyone jumps on my back, I am qualified cycling coach and a regular commuter cyclist into London. However, if all commuter cyclists knew the magnitude of embodied carbon created to form all the basements to store bikes and provide showers, they would be horrified. This, coupled with the many bicycle storage areas that are less than half full, makes me think that it would be better to adapt policy to reduce bicycle storage provision to more reasonable numbers; provide better, secure, safe storage on ground level adjacent to buildings, or allow for the number of bicycle storage spaces to be shared between adjacent developments or local centralised storage areas. It would be a simple, adaptable policy that still has the same net benefit but could reduce the need for new carbon-intensive basements.
The same would be true of building heights and massing, where a few additional storeys could be added to allow for the removal of a basement and therefore all other polices to be met, while still providing a lower carbon building. At some point, the government will need to legislate for targets around embodied carbon, along with other initiatives, such as a Net Zero Carbon Building Standard and the Built Environment Carbon Database. It feels to me that the National Planning Policy Framework is lagging behind other regulatory bodies, and should be updated as a priority to ensure low-carbon buildings are delivered as standard. We don’t have any time to waste.
Tom Webster, Webb Yates Engineers
Source: Architecture Today
