Dormers are projections on a pitched roof consisting of their own small roof, side cheeks and one or more windows. They enlarge the usable area on the attic floor and bring daylight to places where the sloping roof would otherwise be too low. Multiple dormers can be placed on a single roof plane.
Types of dormers
- Flat-roof dormer — the most common variant, with a slightly sloping flat roof; affordable and offers the most interior space
- Gable dormer — with a small pitched roof and two sloping planes; suits traditional houses
- Hipped dormer — with three sloping roof planes; refined appearance
- Trapezoidal dormer — wider at the front than at the back
- Shed dormer — single sloping roof, modern character
- Eyebrow dormer — curved form without side cheeks
- Continuous dormer — extends across (almost) the entire roof width
Construction
A dormer rests on the existing rafters of the roof plane. During installation, some rafters are usually interrupted; their forces are taken over by a trimmer beam. The side cheeks are insulated and clad with zinc, timber or plastic. The front contains the window frame with insulating glass. The connection to the roof plane is sealed with lead or a lead alternative.
Planning permission
In many countries, a rear dormer can be built without planning permission provided it meets size and position requirements. Generally:
- Minimum distance from eaves and verges
- Maximum height and width to remain permitted development
- Front dormers typically require planning approval
- Conservation areas may impose additional restrictions
Application
Dormers are a popular way to make an attic suitable as a bedroom or study. Besides extra headroom, they provide natural ventilation and daylight. They can be prefabricated and installed in a single day, or built on site.
Related terms
- Dormer window
- Roof window
- Gable roof
- Rafter
- Knee wall
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