A dormer is a structural addition that projects vertically from the slope of a roof, creating additional headroom and floor space in the attic while allowing natural light and ventilation through one or more windows.
Types of dormers
Dormers come in several forms, each with a distinct roof shape and visual character:
- Flat-roof dormer — the most common type for maximising interior space. It has a simple flat or very slightly pitched roof and a vertical front wall with windows.
- Gable dormer — features a small pitched roof with a triangular front, giving a traditional appearance.
- Shed dormer — has a single sloping roof plane set at a lower angle than the main roof, often spanning a wide section.
- Hipped dormer — the roof slopes on three sides, producing a compact and visually softer shape.
- Arched or eyebrow dormer — a curved roof that flows smoothly out of the main roof surface, used mainly for decorative effect.
Construction and regulations
A dormer is built by cutting an opening in the existing roof structure, framing the new walls and roof of the dormer, and then finishing with cladding, insulation, and weatherproofing. The connection between the dormer and the main roof is a critical detail — lead flashing or specialised membrane strips are used to prevent water ingress at the junction.
In many regions, smaller dormers can be built under permitted development rights without a full planning application, provided they stay within size limits and do not face the public road. Larger dormers or those on listed buildings typically require planning permission.
Application
Dormers are one of the most popular ways to convert an unused attic into a bedroom, office, or bathroom. They increase usable floor space by pushing the walls outward and raising the effective ceiling height. Beyond the practical benefits, dormers add architectural interest and can increase property value.
Related terms
- Roof house
- Roof light
- Loft conversion
- Roof pitch
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