Scoping out a new overheating index for buildings in the UK

In 2024 the Grantham Research Institute partnered with Shade the UK to begin building the case for creating a user-friendly metric to measure overheating risk in homes and buildings in the UK. Anna Beswick, Candice Howarth and Andy Love explain the rationale for a metric and some of their key findings from work conducted in the London Borough of Islington.

Research led by the Grantham Research Institute has highlighted that more action is urgently needed to manage heat risk in the UK and overheating buildings should be at the top of the priority list. More than half of British homes currently suffer from overheating risk and this is projected to increase to 90% of homes under a 2°C warming scenario. Overheating seriously impacts people, even during periods of moderate heat. Through our project work in the London Borough of Islington (an area at high risk from heat, as we explain below), we heard countless stories from people of all ages and backgrounds that powerfully illustrated the problems of living and working in overheating buildings. This comment from one resident summed up the mood among many:“I would not have moved into this flat if I knew how boiling it was going to get.”

A user-friendly metric of overheating, similar to Energy Performance Certificates which rate a property’s energy efficiency, could support potential tenants and buyers to understand heat risk to buildings before deciding whether to move in. The results could also help building owners, managers and tenants to identify measures that they can take to reduce heat risk, helping to drive investment in retrofitting.

Our work on scoping options for a new heat metric identifies that:

• Existing metrics are not suitable for communicating heat risk to the average person. Feedback from stakeholders is that they are too complex for non-expert users.
• A new metric must demonstrate legitimacy and build trust. This can be achieved by having the metric certified by a trusted institution or body.
• Heat risk information should be easy to access and integrated within existing frameworks such as the Energy Performance Certificate to ensure a single, unified source of climate risk information.
• Policy changes are needed alongside development of a heat metric. This should include changes to existing regulations such as revisions to Part O of the Building Regulations to include and mandate retrofitting to residential and non-residential buildings.
• Funding is needed to support technical development of the heat metric. Our study focused on the London Borough of Islington, a location with one of the highest levels of heat risk in the UK. Further work is needed to conduct a nationwide assessment of heat risk for different types of buildings and to carry out testing and development with users.
• Further work is needed to develop a detailed economic case and secure funding. Our work indicates that while there is likely to be a strong economic case for developing a new, accessible heat metric, more work is needed to develop a business case, including detailed economic and financial analysis.

Scoping work: building-type analysis and firsthand experiences

Shade the UK completed detailed analysis of heat risk for seven building types in the London Borough of Islington. Densely populated inner city boroughs like Islington heat up more quickly and stay hotter for longer than less built-up areas. Heat risk also interacts strongly with socioeconomic vulnerability. This means that areas like Islington that have high levels of deprivation, high numbers of young children and elderly people, and high levels of social isolation are most at risk from increasing temperatures and will likely experience the most severe impacts.

The analysis focused on buildings that are likely to be used by vulnerable groups considered most at risk from overheating: mid- and high-rise apartment blocks including social housing, a care home, school, hospital and prison. Shade the UK created a thermal dynamic simulation model for each type of building. The model factored in solar control glazing, openable windows and doors, and building layout. Sun exposure was also considered and was used to assess how outer building surfaces, including windows and roof areas, would be affected.

This technical analysis was combined with work to collect accounts from Islington residents of their experiences of living and working through the Summer 2022 heatwaves. A range of built environment, local government and community stakeholders also took part in a roundtable event to provide feedback on options for a new heat metric. The experiences shared by residents illustrated how the technical challenges of dealing with heat risk play out in the daily lives of individuals and are important in understanding public perceptions of heat risk and the practical implications and benefits of implementing a metric.

Results: inadequate buildings and considerations for developing a metric

The building assessments provided very strong evidence that Islington’s building stock is not ready to withstand the increasing risk of excessive heat. We have published detailed results in the project report, showing analysis of heat risk across the different types of buildings. The report also includes our review of existing heat metrics and identifies a range of strengths and weaknesses that will be important to consider as work is progressed to develop a detailed case for a new heat metric. Roundtable participants emphasised that communication about the metric should include information on solutions and actions needed to reduce heat risk. Priority should be given to communicating and engaging with those most vulnerable to heat risk to ensure that their voices are heard. Participants were keen to have access to a single metric capturing heat risk information alongside energy performance and other relevant climate risk information. They also considered measures needed to enable people to act on the results of the metric, including the need for financial incentives.

Residents’ accounts are a first in opening up a public dialogue, raising awareness of heat risk and involving those most affected in open and honest discussions about options to reduce heat risk. Stories captured through this project have been carefully curated by Shade the UK and are now a permanent feature on its website and as part of communication and engagement in Islington and beyond.

What happens next?

Overheating of existing buildings is a known risk that successive UK Governments have failed to act on, with research and policy responses repeatedly delayed. While our project with Shade the UK focuses specifically on the potential for a heat metric to contribute to addressing heat risk, the results have wider policy implications. They show once again that we ignore heat risk at our peril and that those who are most vulnerable in society are paying the highest price for delayed action.

The full results of this research are available in the project report: Building Heat-Resilient Neighbourhoods – Shade the UK