Developing net-zero housing policy for Welwyn Hatfield Borough Council

Welwyn Hatfield Borough Council (WHBC) has declared carbon emergency and is committed to decarbonise its housing stock by 2030. However, the Council’s Planning Department continues to give planning approvals for projects that comply with Part L Building Regulations that do not require new buildings to achieve net-zero emissions. The team from the University’s Zero Carbon Lab has established contacts with the Council’s Housing Department and agreed to conduct design simulations on a planning approved scheme consisting of a cluster of six three-bedroom houses in order to investigate how that scheme could be redesigned to achieve net-zero emissions. Four cases were investigated through detailed dynamic simulations: Case A – as per planning approval, Case B – as Case A but redesigned for zero carbon emissions using conventional materials; Case C – retrofit of Case A in ten years to achieve zero carbon emissions; and Case B.1 – as Case B but designed to net-zero carbon emissions using hemp-lime bio-composite material. All cases were evaluated for total carbon emissions, including emissions embodied in building materials arising from extraction, manufacturing, transport to site and construction, as well as operational emissions arising from running the buildings. It became apparent that case C, retrofitted to net-zero operational emissions in ten years, will not achieve cumulative net-zero emissions before the end of the century, while the retrofit cost will be significant. Case B will achieve cumulative net-zero emissions by 2065, and only case B.1, constructed from photosynthetic materials that reduce embodied emissions arising from carbon sequestration during original plant growth, such as hemp, will achieve cumulative net-zero emissions by 2045, but it will cost more to construct than Case B. None of the analysed cases will fulfil the Council’s commitments to decarbonise the building stock by 2030, and only Case B.1, will achieve net-zero emissions before the UK Climate Change Act target date of 2050. This provided evidence base for a report that the team from Zero Carbon Lab submitted to the Council.

In summary, this was new research activity, working in partnership with policymakers, in order to increase the understanding of local, regional and national challenges in responding to carbon emergency and achieving net-zero housing. It facilitated the use of existing research at the University’s Zero Carbon Lab and the exchange of knowledge between the University and the policymakers at Welwyn Hatfield Borough Council. The Council has perceived this research to be of high value in seeking solutions to their strategic net-zero emissions challenges, and has engaged actively in the dialogue with the University. The University Research Assistant on this project is a postgraduate researcher working on his PhD, and the project has created opportunities for him, as well as for the University team, to develop effective communication with policymakers. The work done included detailed design simulations of four different alternative designs, providing the evidence base for policymakers. Thus, this project has fulfilled the majority of the funding criteria and has generated opportunities for new collaboration beyond the funded period.

The impact on the policy arising from this project will result in long term reduction of carbon emissions from housing projects at Welwyn Hatfield Borough Council and, as result of an ongoing dissemination by the University, it will be an example for other local authorities to follow regionally and nationally.