Which dormer or rooflight?

A dormer projects out from the existing roof slope, creating a new vertical wall and window that significantly increases both floor area and headroom. A rooflight sits flat within the plane of the existing roof and mainly introduces daylight, with only a modest gain in usable floor space. In practice, a rooflight is the budget, fast route to a brighter loft; a dormer is the route to a genuinely walkable room with a proper window and outlook.

Rooflights that sit flush within the existing roof plane and don't extend beyond it usually qualify as permitted development and can be installed without a full planning application. Dormers, however, almost always require planning permission because they alter the roofline and change the appearance of the property from the street. There are exceptions — for example, small rear dormers on certain house types may still fall within permitted development limits — but we confirm the exact position for your address during the feasibility visit rather than generalising.

A standard box dormer typically adds roughly 1.5 to 2.0 metres of additional headroom across the new floor area, which is usually enough to bring the loft comfortably above the 2.2–2.3 metre minimum required for a habitable room. The exact figure depends on your existing roof pitch, the depth of the dormer projection and how the floor is cut into the existing slope. We measure all three on-site and tell you what you can realistically expect before any design is committed.

Yes, and it is a common and effective combination. A main rear dormer creates the usable room and headroom, while supplementary rooflights on the opposite slope or in the side bays distribute daylight more evenly across the new floor and reduce the risk of a dark, single-aspect space. We design the mix together so the rooflights complement rather than compete with the dormer.

Overlooking and right-to-light are real considerations, particularly on terraced streets where properties sit close together. We assess separation distances, window positions and sightlines during the design phase and factor in privacy glazing, higher sill heights or adjusted dormer widths where needed. Planning officers will also look at this, so getting it right early avoids objections and delays later.

Dormer roofs have more junctions and flashings than a simple roof slope, so they benefit from an annual inspection of the leadwork, flashings, roof coverings and valley gutters. We provide a written maintenance guide at handover and offer annual check-up visits, particularly important given that most of our dormer work is on period stock where the roof geometry is more complex than on modern properties.