Britain’s new homes face 2050s heat test as experts warn of overheating crisis

Updated industry guidance says new homes should be tested against 2050s heat, with better ventilation, more shade, tighter bedroom checks and less excessive glazing to stop properties becoming dangerously hot

New homes in Britain should be designed with better ventilation, more shading and less excessive glazing under updated guidance aimed at stopping properties overheating as temperatures rise.

The recommendations say homes should be tested against weather expected in the 2050s, with tighter checks on bedrooms, where high overnight temperatures can make it harder for people to sleep.

The update is designed to make overheating assessments tougher at the planning stage and reduce reliance on assumptions about how residents might cool their homes, including opening windows or using ventilation at the right time.

According to the Chartered Institution of Building Services Engineers (CIBSE), many new and existing homes are already vulnerable to excessive indoor temperatures because of extensive glazing, weak ventilation strategies and designs that do not properly account for future climate conditions.

The new guidance is intended to push designers towards cooler homes that rely on layout, shade, airflow and ceiling fans before air conditioning is needed.

It comes as a new heatwave starts to build across parts of the UK, with forecasters warning temperatures could reach 33C or 34C from the weekend.

The guidance was issued on Monday by CIBSE, the industry body that oversees TM59, a methodology used by designers and the wider construction industry to assess whether new homes and major residential refurbishments are likely to become too hot.

It is referenced in Part O of the Building Regulations and is widely recognised as a key industry resource for assessing overheating risk in residential buildings.

Ahmed Hegazi, head of knowledge and digital at CIBSE, said: “Overheating is no longer a future risk – it’s a present reality for households across the UK, and the built environment sector needs authoritative, evidence-based guidance to respond.

“This revision of CIBSE TM59 represents CIBSE at its best: rigorous research, a decade of practitioner experience, and a clear-eyed view of where regulation and design practice need to go.

“It gives industry and policymakers alike a robust foundation for delivering homes that remain safe, comfortable and resilient in a warming climate.”

The updated guidance was produced by CIBSE in collaboration with engineering consultancy Arup and Loughborough University.

CIBSE said the new version draws on academic research, industry experience and testing across real projects.

It includes new advice on how to assess overheating in bedrooms and updated modelling guidance for ceiling fans, which can help improve comfort using less energy than mechanical cooling systems.

Becci Taylor, director and UK housing property lead at Arup, said: “When CIBSE TM59 was first developed, there was no consistent way to assess overheating risk in homes.

“This updated version builds on years of practical application, new research and industry insight in applying overheating assessments.”

Antonietta Canta, associate at Arup, added: “The updated CIBSE TM59 reflects our growing understanding of how buildings perform in a warming climate.

“It provides a standardised approach to assessing overheating risk to create homes that remain comfortable, resilient and fit for the future.”

According to CIBSE, the guidance is relevant to residential design, natural ventilation, building performance, sustainability, retrofit, refurbishment, climate resilience and government policy.

Professor Kevin Lomas, of Loughborough University, said: “The new version of CIBSE TM59 provides a blueprint for the assessment of overheating risk in new dwellings and dwellings subject to major refurbishment.

“The revision of CIBSE TM59 is set against the backdrop of Part O of the Building Regulations, which relies on CIBSE TM59 to define how models are to be used for overheating analysis.

“The revision incorporates the outcomes of recent research, some of which CIBSE funded – a new criterion defines overheating in bedrooms when people are sleeping, and ceiling fans are introduced as an effective passive means of comfort cooling.

“The new, more rigorously-defined assessment methodology, should improve the consistency and clarity of overheating analysis and reporting.

“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.”

For some areas, this week could see the third heatwave of the year, with the hottest conditions expected across southern and eastern England as high pressure builds from the Azores.

Yellow heat health alerts have been issued by the UK Health Security Agency for the East Midlands, West Midlands, east of England, London, south-east England and south-west England from Saturday until July 11.

The alerts warn of an increased health risk, particularly for older people and those with underlying conditions, as temperatures climb above 30C in many areas.

READ MORE: Britain to rank among Europe’s hottest places as 40C heatwave closes in. Forecast peak put parts of England and Wales among Europe’s hottest places this week, below the worst-hit areas of France and Spain and above or level with Rome, Athens, Marseille and Nicosia.

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