Dormer
A dormer loft conversion builds out from the existing roof slope to add headroom and usable floor space. Dormers can sit at the rear, side or front, and a flat-roofed rear dormer is common on semi-detached and terraced houses. Rear dormers can often be built under permitted development if they stay within the volume and design limits, but a dormer on the main roof slope facing a road, or on a home on designated land, normally needs planning permission.
What to Know About Dormer
- Adds headroom and usable floor space compared with a rooflight conversion
- Full-width rear dormers make the most of the room size
- Rear dormers can often be built under permitted development if they meet the limits
- Suits many semi-detached and terraced houses
- Extra space can make room for an en-suite, which adds to the cost
Price Guide
£40,000–£75,000
Typical UK range, last reviewed September 2026. A guide, not a quote.
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Frequently Asked Questions
How long does a dormer loft conversion take?
Checkatrade's March 2026 cost guide puts a typical 30m² dormer conversion at around 10 to 12 weeks on site, once any planning permission is in place. The time depends on the size of the dormer, the structural work and whether you are adding a bathroom.
Will a dormer change the look of my house?
A rear dormer is usually less visible from the street than a side or front dormer. Under permitted development the materials must be similar in appearance to the existing house, and a dormer on the principal roof slope facing a road is not permitted development. A designer can show you how the dormer will look before you decide.
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