Architecture Public knowledge base

Reviewed 25.10.2026England focus

Jasmine Gokmen
In force · under reviewVentilation & Overheating

Approved Document O: Overheating

Mitigating summer overheating in new residential buildings

Requires new residential buildings to limit overheating through passive design, using either a simplified glazing and shading method or dynamic thermal modelling to CIBSE TM59.

Also known as: AD O, Approved Document O, overheating

Jurisdiction
England
Document type
Statutory guidance
Edition
2022 edition
Source updated
15 June 2022
Applies from
15 June 2022
Topic
Ventilation & Overheating

Key requirements

  • Applies to new residential buildings, not to extensions or changes of use.
  • The simplified method limits solar gains by orientation, glazing area and shading.
  • The dynamic method requires a TM59 assessment and a report for building control.
  • Passive measures must be used as far as reasonably practicable before mechanical cooling.
  • A full technical review of Approved Document O was announced in 2026.

Performance at a glance

Methods
Simplified / dynamic
Dynamic test
CIBSE TM59
Cooling
Passive measures first
Review
Announced 2026

Applies to

New residential buildings in England, including flats and houses.

Official source

GOV.UK — Approved Document O

Open official source

Related records

TM59 · CIBSE TM59 overheating assessmentPart F · VentilationPart L · Conservation of fuel and powerPart K · Protection from falling, collision and impact

Reviewed 25 October 2026. This summary is an editorial reference, not legal advice. Check the current official text and confirm the approach with building control before relying on it. Browse all 35 records.