Approved Document O: Overheating
England-focused reference checklist
Editorial source review: 2026-10-17
https://saeedazarshab.com/articles/england-building-regulations/approved-document-o/

INDEPENDENT GUIDANCE — not project-specific legal/design advice or a compliance certificate. Check the official current requirements and applicable transition.

Part O addresses overheating in new residential buildings within its scope. It is not a blanket retrofit rule for all existing buildings. The assessment route and mitigation need to reflect the actual design, including glazing, shading and the practicality of removing excess heat without creating other safety or usability problems.

WHAT TO CHECK
[ ] Confirm scope, applicable dates and the assessment route with the responsible designer.
[ ] Check that the assessment matches the proposed building, orientation and room arrangements.
[ ] Coordinate opening windows or other mitigation with noise, security, falling risks and usable access.
[ ] Review changes that affect glazing, shading or the removal of excess heat.
[ ] Keep the assessment and the information needed by occupants to use the building as intended.

RECORDS TO KEEP
- Overheating assessment and design assumptions
- Coordinated mitigation details and changes
- User information on the intended strategy

WHEN TO GET SPECIALIST HELP
Get competent assessment advice for uncertain scope, difficult sites or designs whose mitigation depends on unrealistic occupant actions.

SCOPE AND EDITION
Landing updated 15 June 2022 and links corrected guidance and official FAQs. Confirm the project transition and assessment route. Do not present Part O as a blanket requirement for all existing buildings. Coordinate overheating mitigation with noise, security, safety and ventilation.

OFFICIAL SOURCES
GOV.UK — Approved Document O
https://www.gov.uk/government/publications/overheating-approved-document-o

Official Approved Document O FAQs
https://www.gov.uk/guidance/approved-document-o-overheating-frequently-asked-questions

Contains public sector information licensed under the Open Government Licence v3.0, except where otherwise stated. Original practical summary by Saeed Azarshab.
https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/