As part of the National Interdisciplinary Circular Economy Research (NICER) programme, City Science was awarded funding to develop a circular design tool, to determine the total carbon impact of a new housing development over its whole lifetime. Our tool aims to support masterplanners, local authorities and housing developers; enabling them to estimate the lifetime carbon impact of their development quickly and easily at any stage in the planning process.
The construction sector has long been recognised as one of the most difficult to decarbonise. Alongside the hard-to-remove embodied carbon in building materials and the high energy processes required in construction, there is incredibly high demand for new houses, with the government target standing at 300,000 a year, by the mid-2020s. This has the potential to use a large proportion of the UK’s remaining carbon budget. However, the sector is evolving rapidly. Proof of sustainable credentials are now essential when developers bid for new contracts and local authorities are quickly incorporating ambitious targets around energy efficiency & embodied carbon in their local plans and design codes. A significant problem, which we are aiming to address, is when planners are assessing carbon impact, their approaches are not standardised and no developers currently consider the full scope of their carbon impact. Energy efficiency & embodied carbon and considered entirely separately, despite being intrinsically linked while transport and the need for adequate local facilities to serve new residents are rarely considered at all. We proposed that a tool could be designed to calculate the cradle-to-grave emissions of any new development, massively reducing the resources required to make such calculations; providing planners with robust evidence to help them make better decisions and producing a standard framework for holistic property carbon calculations.
Our approach to calculating the whole lifetime emissions of a development split emissions into 4 key categories:
• Construction: Embodied carbon figures were determined from the mass of each construction material, using per Kg figures from the Inventory for Carbon & Energy database and lifecycle analysis papers. These calculations were designed to align with the Building Research Establishment Environmental Assessment Method (BREEAM) carbon assessment methodology. Maintenance, demolition & landfill emissions were also assessed here.
• Energy: A steady state heat loss calculation is performed on each building, using location specific climate data. This calculation aligns with the government’s Standard Assessment Procedure (SAP) calculations. Total energy usage calculated can then be converted to an embodied carbon figure using the government standard conversion factors for electricity & gas.
• Transport: The impact of new residents' travel from the property to places of employment, retail & leisure facilities was determined using a gravity model that was calibrated using Census and local travel survey data. 9 different travel modes were incorporated, determining total travel mileage and total carbon emissions.
• Local Facilities: New developments add significant demand to local facilities such as shops, schools & hospitals and may require the construction of new amenities. Our model determined the increase in load on facilities and the resulting increase in emissions on a per person basis, using data from cutting-edge research.
As our tool is intended for use at multiple points in the design process, it was crucial that it could be flexible to a variety of different data inputs. As such, our model was built with in-filling capabilities. Based on the location and type of property, where information about the construction is not provided, the most likely construction type or material is assumed. This allows the model to have a high degree of accuracy at the construction phase but be quick and easy to use at the early planning stages. No equivalent tool is available for planners to forecast the emissions of developments they are considering.
In addition to designing a commercially appealing tool, the project also allowed us to use the tool to research the most effective interventions when designing sustainable houses. Figure 4 shows an example, where we looked at the carbon impact of construction and operation for different choices of wall material. The addition of insulation to a cavity brick or stone construction will increase the material emissions, something that could be penalised if only embodied emissions were determined but massively reduces the energy emissions, making it a clearly beneficial intervention. This is clear evidence for why carbon calculations need to be holistic and targets should not just be set for one emission category. Our Circular Design tool is already being used to influence local housing policy through our projects with local authorities in Uttlesford & the South of Bedford.
In Uttlesford, our tool has been used to set property-type specific carbon impact per floorspace targets in their new design codes. The targets are ambitious, helping the authority reach their net-zero targets but are realistic for all properties thanks to the property-type specific targets made possible by our Circular Design tool.
In the South of Bedford, our tool is being used to assess the carbon impact of construction in the region and forecast how policy interventions will alter future carbon emissions. The tool will make it possible for us to quickly produce far more accurate carbon mapping & forecasting, that would previously not have been possible.