New TM59 Update - Overheating Risk in Dwellings

Higher temperatures and more frequent and intense heat waves are inevitable as the UK climate warms. High indoor summertime temperatures result in diminished health and well-being and can be fatal, especially for people with underlying health problems. In 2026, the Climate Change Committee elevated the ‘Risks to buildings and communities from heat’ into the highest risk category - ‘Critical Action needed’.

TM59 provides the industry blueprint for assessing overheating risk in new dwellings and major refurbishments using dynamic thermal models. It explains how models should be used, the assumptions to be made, and defines a three-stage overheating assessment strategy. It is applicable to houses, apartments, sheltered accommodation, care homes, student accommodation, prisons, and bedrooms in hotels and hospitals, etc. 

By mandating that all homes be tested under unconstrained conditions using 2050s weather data, the updated TM59 guidance places a strong emphasis on optimising passive design from the outset. This shifts the focus towards inherently resilient homes that can maintain summer comfort into the future without relying on active cooling.

Download the documents below to read more:

TM59 compliance checklist

TM59 overheating risk in dwellings - design stage methodology

TM59 weather file requirements