21 July 2026
With another spell of hot weather across the UK, overheating in homes is becoming more than just a summer talking point.
On 6 July, CIBSE published an update to its TM59 methodology, introducing a 2050s climate scenario in place of the previous 2020s weather data. The update also includes revised approaches to assessing bedroom overheating and the use of ceiling fans, reflecting the latest research into keeping homes comfortable as our climate continues to change.
For developers, architects and design teams, it reinforces the importance of considering overheating early in the design process. Decisions around site layout, orientation, glazing, shading and natural ventilation all influence how a home performs, making early coordination between the wider design team more important than ever.
The update also reinforces the importance of considering overheating and acoustic performance together where natural ventilation forms part of the design strategy.
Natural ventilation, such as opening windows, is one of the principal passive cooling strategies considered within TM59 assessments and supported by Part O. However, where developments are located close to busy roads, railways or commercial uses, external noise can influence whether opening windows can provide an acceptable acoustic environment, particularly during the evening and overnight.
Our Acoustic Consultants assess the external noise environment to determine whether opening windows for natural ventilation can provide an acceptable acoustic environment for future occupants. Those findings help inform the wider overheating assessment, enabling the design team to determine whether additional mitigation or alternative ventilation strategies may be required. This is also an area that continues to evolve at an industry level, with our Acoustic Consultant, Harry Johnson, contributing to the Future Homes Hub Part O Liaison Group. Working alongside the Building Safety Regulator and the Ministry of Housing, Communities and Local Government, the group is helping to shape future guidance on topics including noise, shading, safety measures and planning implications.
Considering these factors early helps avoid conflicts between thermal comfort and acoustic performance, supporting a more coordinated design approach from the outset.
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