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What is Approved Document O?

Part OPublished on 15th December 2021 and coming into force on 15th June 2022, the government has set out its new requirements for Part O (overheating) of the Building Regulations and the supporting Approved Document for new dwellings in England.

Applying only to new residential buildings, new residential buildings must be designed and constructed in such a way as to limit unwanted solar gains in summer and provide an adequate means to remove excess heat from inside. Two methods of assessment are given in Approved Document O:
  • Simplified method, related to location, dwelling type, glazing area and presence of cross-ventilation
  • Detailed thermal analysis method, involving calculation of the risk of overheating
For the simplified method, England is split into two:
  • Moderate risk locations (England excluding higher risk parts of London)
  • High risk locations (urban and some suburban parts of London)
As buildings located in some Central Manchester postcodes may also experience elevated night-time temperatures, they should be considered high risk.
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