Part O Overheating Assessments for New Homes

Part O Overheating Assessments for New Homes

Part O of the Building Regulations limits overheating in new homes. Every new house, flat, care home and student residence in England has needed an assessment since June 2022. The simplified method is the quickest and cheapest route, and we tell you early if your design will need a dynamic model instead.

How the simplified method works

It checks two things for each home:

• Glazing. The glazed area is limited as a percentage of floor area. The limit depends on which way the most glazed side faces and whether the home has cross-ventilation.
• Openings. Windows and doors have to provide a minimum free area so heat can escape.

Homes in the high-risk area, which covers much of London, have tighter limits and also need shading or solar-control glass.

When the simplified method will not work

• Heavily glazed designs, large sliding doors or rooflights
• Single-aspect flats with no cross-ventilation
• Sites where noise, security or air pollution mean bedroom windows cannot be left open at night
• Blocks of flats with communal heating pipework running through corridors

These need a dynamic model. We check this before we start, so you do not pay for two reports.

What we need from you

• Floor plans and elevations with window sizes and how each window opens
• The site address and orientation
• Any noise report or security constraint, such as ground-floor bedrooms

Questions we get asked

Does Part O apply to extensions and conversions?
No. Part O covers new residential buildings. Some councils still ask for an overheating check at planning, and we can provide one.

What if my design does not pass?
We tell you what to change: smaller or different glazing, shading, or more opening area. If none of that suits the design, a dynamic model gives more freedom.

Is Part O changing?
Not yet. The government has announced a full technical review of Part O. Until that is finished, the current edition applies.

Send us your drawings by email or WhatsApp and we will come back with a quote and a turnaround time.