Can I build a dormer without planning permission?

Permitted development rights are a national grant of planning permission for common building work, so the council does not have to be asked first. Class B of Schedule 2, Part 1 of the General Permitted Development Order 2015 deals with additions and alterations to a house roof that make the house bigger. A rear dormer, the box that lifts out of a back slope to give a loft room headroom and a window, is the standard example. The rights belong to the dwellinghouse, so they are tied to the house and its roof as they stood originally.

Class B is a list of limits, and a dormer has to pass every one of them. Fail one and you apply for planning permission instead, which is an ordinary process, not a refusal. Even where Class B applies, the work still has to satisfy the Building Regulations, which is a separate set of rules with its own test and its own application.

Class B.1 sets the main tests. The new work may not rise above the top of the existing roof. It may not sit forward of the original roof slope that makes up the principal elevation and faces a highway. The added roof space may not exceed 40 cubic metres on a terraced house, or 50 cubic metres on any other house. Anything involving a verandah, a balcony or a raised platform is out, and the rules also exclude work that involves chimneys, flues or the soil pipes that vent a drain.

Class B.2 attaches conditions. Materials need to look similar to those on the existing house. The edge of the enlargement should, so far as is practicable, stay 0.2 metres or more back from the eaves, which is the lower edge of the roof. A window in a side wall of the dormer has to be obscure-glazed, and kept closed, except where the opening section sits 1.7 metres or more clear of the floor inside. People often miss this last point when they draw a window beside the bed.

Class B.1(f) switches the right off when the house stands on article 2(3) land. That is the legal label for a group of protected areas, and it covers conservation areas and areas of outstanding natural beauty. The North Wessex Downs and the Cotswolds have been called National Landscapes since 22 November 2023, though the legal designation and its protections have not changed. A dormer there is therefore not permitted development, and a planning application is required.

The position differs from that for roof windows. Roof windows come under Class C, and can still be permitted development on that protected land, with conditions. Dormers get no such relief. In a National Landscape the council decides the application, and the landscape body only advises. If you think your road may be in a conservation area, raise it with the planning department that serves your street before paying anyone for drawings.

Article 2(3) land is not the only catch. Listing brings its own regime, because works that change its special character need consent of their own, whatever Class B appears to allow, and proceeding without that consent is an offence. Government planning guidance adds that a council can withdraw particular permitted development rights across a defined area using an Article 4 direction, and that a condition written into an earlier permission may remove them from one property.

So there are three checks before any dormer is designed: is the house listed, is it in a protected area or an Article 4 area, and does the paperwork from when it was built carry a condition? If the answer to any of them is yes, speak to the planning team before spending money on drawings, and keep their reply on file for whenever you come to sell.

Permitted development does not remove the Building Regulations. A dormer opens up the roof structure, so it needs structural design, insulation to current standards and proper means of escape. Under Part L, a new or replaced roof in an existing home is limited to 0.15 W/m²K of heat loss, and a window to 1.4 W/m²K or Band B for window energy rating. Where the loft room sits above a two-storey house, escape from the new storey is a question for your building control body too.

What the roof is built from matters here, because a dormer in a trussed roof is a bigger structural job than one in a traditional cut roof. Our page on cut roofs versus trussed roofs explains why. Covering and pitch influence the design as well, so our notes on low-pitch tiles may help you plan the dormer roof itself, since a flat or shallow dormer top needs a different covering.

We build the weatherproof shell: the cheeks, the dormer roof, the lead and the tiling, tied properly into the existing slope. Where consent comes into it, we explain what is needed, and we deal with the Building Regulations notification when the work is notifiable. The planning decision itself belongs to the council, so we send you to its planning team rather than give you a ruling. For a sense of covering costs, see tiled roof repair cost.

Our survey shows you your own roof in photographs, our price arrives in writing, and a 10-year workmanship guarantee backs what we build. For related roof-shape questions, visit the pitched roofing hub.