Do you need permission for a roof window?

A roof window lies in the plane of the slope, so on the front or back of a house it rarely comes near the 150 mm limit. The rule that catches people is on the side. Any window on a roof slope forming a side elevation of the house must be obscure-glazed and non-opening, unless the parts that open are more than 1.7 m above the floor of the room it is in. A semi-detached or end-terrace loft room with a gable on one flank and a slope on the other is where this comes up.

It follows that a window in a side slope that you want to open and see out of needs either that height above the floor or a planning application. The height is measured from the floor of the room it serves, so a low top-hung window in a chalet bedroom is likely to fail it. We read the slope orientation from your plans at the first visit and mark which slope faces which boundary, since moving a window from one slope to another can change the answer.

Building Regulations treat any fresh roof opening as building work, because it affects the structure and the energy performance of the house, and sometimes fire safety and escape. When a roof window replaces an existing one, the new unit has to meet the window limit of 1.4 W/m²K under Part L, or reach Window Energy Rating band B at minimum. A rooflight on a kerb has a looser limit of 2.2 W/m²K, which is why the two products are told apart.

We handle the Building Control notification where the work is notifiable, and the local authority or a registered building control approver signs it off. Our page on skylight building regulations sets out what is inspected.

A flat or maisonette has no householder permitted development to rely on, so a roof window in a top-floor flat needs a planning application, and a leaseholder will usually need the freeholder's agreement as well. Homes that began as offices, shops, barns or comparable buildings and became houses through change-of-use permitted development are in the same position. Separately, the original planning permission for a house may carry a condition withdrawing its rights, and the decision notice will show it, so read that before assuming anything.

A conservation area on its own does not remove the right to fit a roof window; only an Article 4 direction does, and our answer on Article 4 and rooflights covers how to find out. A listed house still has the right on paper, yet a new or altered roof window will almost always need listed building consent. See rooflights on listed buildings.

Putting a bedroom in the roof brings escape into play. On a bungalow or chalet bungalow, a roof window can serve as the escape window for rooms in the roof if the opening is at least 0.33 m², at least 450 mm wide and 450 mm high, with the bottom of the opening no more than 1,100 mm above the floor, and the window stays open without being held.

On a two-storey house, a loft conversion creates a storey more than 4.5 m above ground, and a roof window in it is not accepted as the escape route. That normally calls for a protected route down the stairs. A new window has to be sized for the light you want and for these tests, so check both before ordering. A loft conversion also touches the stairs, the structure and the fire protection, so the roof window is one line among several on the Building Control file. To see how pitch affects the choice, read minimum pitch for a roof window, or go back to the main roof windows section. To have your slope assessed, book a free survey.