CIBSE has published updated TM59 guidance to help professionals assess and reduce overheating risk in new and refurbished homes.
The updated CIBSE TM59 Overheating risk in dwellings: A design stage methodology, produced with Arup and Loughborough University, revises the methodology referenced within Part O of the Building Regulations for evaluating overheating risk in residential buildings.
CIBSE said many new and existing homes remain vulnerable to excessive indoor temperatures because of extensive glazing, insufficient ventilation strategies and designs not adequately adapted to future climate conditions.
Among the changes, all homes must now be assessed under unconstrained conditions using future weather files representing the 2050s climate, placing greater emphasis on passive design measures at the earliest stages of development. The revision also introduces an updated approach to assessing bedroom overheating, informed by research from Loughborough University, and revised modelling guidance for ceiling fans as a low-energy comfort measure.
The guide was authored by Susie Diamond of Inkling (lead author), Becci Taylor and Antonietta Canta of Arup, and executive edited by professor Kevin Lomas of Loughborough University.
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.”
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, said: “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.”
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.”
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