The government has introduced Approved Document Part O, a building regulation document addressing overheating in new residential dwellings and buildings where people sleep overnight. The document was set out in guidance published on 24 January 20221.
Part O applies to new build homes and buildings where people sleep overnight, and does not affect pre-existing buildings or commercial spaces1. It sets out two methods of compliance. The first, the simplified method, considers the size and orientation of glazing and compares the glazing area to the floor area, with window opening areas also considered to deliver suitable purge ventilation1. The second is Dynamic Thermal Analysis (CIBSE TM59), which predicts the risk of overheating and offers a range of strategies for reducing that risk1.
Stroma, an independent built environment consultancy, reported three key findings on how the simplified method is likely to perform in practice1:
| Finding |
|---|
| Most single aspect apartments will fail the simplified method |
| Houses with crossflow can pass the simplified method, but window openings likely to need to be increased |
| Schemes with communal heating systems cannot be assessed via the simplified method |
Stroma said the effect of these findings would be increased demand for TM59 overheating assessments1.
"The document applies to new build homes and buildings where people sleep overnight, leaving pre-existing buildings and commercial spaces unaffected."
The document follows a period in which homes have become more insulated and glazing systems have achieved greater thermal performance ratings, which Stroma said leaves residential dwellings facing the risk of uncomfortable living temperatures during warmer months1. Stroma's director of energy services, Andy Mitchell, discussed the changes to building regulations and overheating on the MailOnline podcast The Andrew Pierce Show, and also spoke to The Telegraph about how Part O would affect the number of conservatories in British homes1. The content of those interviews is not reported in the source.
Why it matters for households
Overheating is a comfort and health issue as well as an energy one. A home that traps heat in summer may be cooled by opening windows, running fans or installing air conditioning, all of which affect how much energy a household uses and how much control it has over its own indoor conditions. Part O applies only to new build homes and buildings where people sleep overnight, so households in existing properties are not covered by its requirements1. For buyers of new homes, the compliance route chosen by a developer shapes the design: glazing size and orientation, window opening areas and crossflow ventilation all feed into whether a dwelling passes the simplified method, and single aspect apartments and schemes on communal heating are the cases most likely to need the more detailed TM59 assessment1. Further detail on the practicalities of summer heat in homes is set out in the site's guide to overheating and hot weather in homes, and the wider regulatory picture sits under regulation and policy. For households in Wales, building policy is devolved, as covered in energy and buildings policy in Wales.
What happens next
No dated next steps are reported in the source.