Ventilation in Refurbished and Extended Buildings

What This Requirement Covers

When building work is carried out on an existing dwelling (extension, conversion, or refurbishment), the ventilation provision must be reviewed and, where necessary, upgraded to comply with Approved Document F. The general principle is that the ventilation should be no worse than before the work, and new rooms must have adequate ventilation.

Key Requirements

Extensions

1. New kitchens, bathrooms, and utility rooms in an extension must have extract ventilation meeting the rates in Approved Document F
2. New habitable rooms must have purge ventilation (openable windows) and background ventilation (trickle vents)
3. If the extension blocks an existing window or vent, equivalent ventilation must be provided to the affected room
4. The existing ventilation system may need to be extended or supplemented

Replacement Windows

1. When windows are replaced, trickle ventilators must be provided to at least match the existing ventilation provision
2. Where the original windows had no trickle vents (older properties), the requirement is to provide equivalent background ventilation area to the original windows' adventitious ventilation
3. In practice, this usually means fitting trickle vents with a minimum 5000 mm² equivalent area per habitable room

Conversions (Change of Use)

1. When a building is converted to residential use, the ventilation must comply with Approved Document F for new dwellings
2. This may require installing mechanical extract ventilation, MVHR, or a passive stack system
3. Existing openable windows may satisfy the purge ventilation requirement

Loft Conversions

1. New habitable rooms in the loft must have purge ventilation (roof windows or dormer windows)
2. Extract ventilation to any new bathroom or en suite in the loft
3. Background ventilation (trickle vents) in all new windows

Practical Compliance Tips

1. Assess the existing ventilation provision before designing the extension or conversion
2. When replacing windows, always include trickle vents even if the original windows did not have them
3. In kitchen extensions, specify an extract fan or cooker hood ducted to outside (not a recirculating hood)
4. For loft conversions, ensure at least one roof window or dormer provides purge ventilation (1/20th of floor area)
5. When blocking up existing windows or vents as part of an extension, provide alternative ventilation to the affected room
6. Submit the ventilation strategy to Building Control with the building regulations application
7. Commission extract fans and MVHR systems and provide flow rate measurements for Building Control