Dormer windows and other roof extensions

This section covers additions or other alterations to roofs, most commonly involving dormer windows, but also including an extension built on top of an existing single storey garage attached to a two storey house.

You will not need planning permission, provided that:

  • the alteration would not be on a roof plane that forms part of the principal elevation of your house, or a side elevation that fronts a road;
  • the alteration is more than 10 metres away from the property boundary it faces;
  • its width would be less than half the total width of the roof plane, measured at the eaves;
  • no part of the alteration would be within 0.3 metres of any edge of the roof plane; and
  • it would not be higher than the highest point of the existing house roof.

You will need planning permission if your house is a listed building or is located in a conservation area. If your house is a listed building you will also need listed building consent.

A building warrant will be required for any extension that includes an alteration to your roof.