What is Approved Document Part O of Building Regulations?
The updates to Building Regulations Approved Document Part O came into effect in June 2022 to address overheating in buildings.
‘Overheating’ is approached on a basis of prevention and remedy:
- Prevention: by limiting the amount of direct sunlight through windows and glazing
- Remedy: with a provision to quickly remove excess heat from inside a room when it gets too hot
Part O is also concerned with excess heat caused by heating pipes and not having control of heating - usually for apartment blocks with between floor pipes and communal heating.
To achieve Part O regulations, windows and glazed areas are limited to a maximum size depending on:
- The floor area of the room
- The direction they face (south, north, east, west)
- Cross-ventilation inside the building (opening windows on opposite facing walls)
- If the building is in a high-risk area (London postcodes being the highest risk)
In high-risk areas, the use of external shading will be required (explained below).
Under Part O, what is considered as ‘Overheating’ is calculated by two methods:
- The Simplified Method
- Dynamic Thermal Modelling
Note that Approved Document Part O only applies to new build domestic buildings. Extensions and conservatories added to a property after it has been built do not come under the requirements of Part O.
Replacement windows and conservatories as an addition to existing houses are not affected by Part O.