Part O · England · Free to use
Part O overheating calculator: simplified method
Glazing limits and minimum free area for new homes, by location risk, orientation and cross-ventilation.
Approved Document O (2021)
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High risk covers the urban London and Manchester postcodes in Appendix C. Everywhere else is moderate.
Openings on two opposite façades.
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Part O · Result
Meets the simplified method
No dynamic thermal modelling needed for this flat.
Checks passed- Glazing, whole flat: Checks passedmax 15% of floor area14.4%
- Glazing, most glazed room: Checks passedmax 22% of room area21.2%
- Total free area: Checks passedmin 7.28 m² (greater of 6% floor or 70% glazing)7.4 m²
- Bedroom free area: Checks passedmin 1.63 m² (13% of room)1.7 m²
- Equivalent area of each opening must meet or exceed its free area (para 1.12).
- Also check security, noise and guarding of openings (Section 3).
Clauses this relies on
Source edition and scope
Approved Document O (2021).
This is a preliminary check of the conditions shown. Confirm the edition, project circumstances and any additional requirements with your architect or building control.
A design aid, not legal advice. Checked against the Building Regulations 2010 for England; confirm with building control.