New guidance tests homes against 2050s climate scenario

It’s getting hot out there and that can mean dangerous temperatures indoors.

Last month, the Climate Change Committee warned that 92% of UK homes will be at risk of overheating by 2050.

Building Regulations, frequently criticised for being out of date, have been playing catch up. In 2022, Approved Document Part O was launched to address overheating in new homes. 

However the thermal assessment method on which Part O relied – CIBSE TM59 – was based on a 2020s weather scenario from 2011-2040 and a medium level of emissions.

Now the model has been updated, requiring all new homes and major housing refurbishments to meet the 2050s climate scenario.

The widely recognised CIBSE TM59 Overheating Risk in Dwellings: A design stage methodology has been updated in collaboration with Arup, Inkling and Loughborough University to reflect the latest research based on climate predictions for 2041-2070.

The latest version also includes revised modelling guidance for ceiling fans and has updated its approach to evaluating bedroom overheating, taking into account the latest research.

CIBSE TM59 is referenced in Part O, which applies to new-build homes only. It does not address other building types, extensions or conservatories added to residential buildings or buildings undergoing a change of use to residential.

Part O also requires that all low-energy, passive means of cooling – for example, shade and ventilation – are incorporated first, so that projects do not rely solely on mechanical cooling. This is intended to reduce reliance on air conditioning and use less energy.

In contrast, the UK Climate Change Committee has said it now thinks passive strategies are insufficient to prevent overheating. It has called for investment in air conditioning and heat pumps to protect public health, calling for all care homes and hospitals to install air conditioning within the next 10 years, and all schools within 25 years.

But the authors of the CIBSE guidance believe passive design will be sufficient for homes. Co-author and professor Kevin Lomas, Loughborough University, said: “Using the CIBSE TM59 methodology, dwellings in the UK, including in London, can be designed to stay comfortable using purely passive measures right up to the 2050s.”

Summer temperatures are expected to exceed 40C in all parts of the UK by 2050.