Do I Need Planning Permission for a Dormer Window?
Rear dormers usually fall under Permitted Development. Front dormers almost always need planning permission. The rules depend on which direction the dormer faces, how much volume it adds, and whether your property is in a designated area.
PD rules for dormers
PD rules for dormers
Under Permitted Development, you can add a dormer if: it does not extend beyond the plane of the existing roof slope facing a highway, the total volume added (including any previous loft additions) does not exceed 40m³ (terraced/semi) or 50m³ (detached), it does not raise the existing ridge height, materials match the existing house, and it does not include a balcony or veranda. These rules effectively allow most rear dormers but prohibit front dormers.
Front dormers
A dormer that extends beyond the roof slope facing a highway needs planning permission. This catches most front dormers and side dormers on corner plots. The planning officer will assess bulk, design, and impact on the streetscene. Sympathetic design (matching materials, modest scale) improves approval chances.
Conservation areas and National Parks
In conservation areas, dormers on any roof slope facing a highway need planning permission (the same as elsewhere, but enforced more strictly). In the New Forest National Park, all dormers on front-facing roof slopes require planning — and the NFNPA applies strict vernacular design requirements. In Dorset AONB areas, side dormers may also be restricted.
Common questions
Frequently asked questions
Extension guides
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Planning permission rules for dormer windows — rear vs front dormers, PD volume limits, conservation area restrictions, and NFNPA rules explained.
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