What Is a Dormer Loft Conversion?

A dormer loft conversion adds a structure that projects out from the slope of your roof, with vertical walls and a window facing out. Inside, it turns a cramped triangle of loft space into a room you can stand up in across most of the floor. For many London terraces and semi detached houses, a dormer is the most practical way to add a bedroom and bathroom without giving up any garden.

Types of dormer

• Rear dormer: the most common type, built across the back roof slope. It usually gives the most space for the cost.
• Full width dormer: runs the whole width of the rear roof for maximum floor area.
• L shaped dormer: popular on Victorian terraces with a rear outrigger. One dormer sits on the main roof and another on the outrigger roof, joined to form an L. It often creates space for two bedrooms or a bedroom and generous bathroom.
• Pitched or gable fronted dormer: smaller, with a pitched roof, often used where appearance matters, such as on a front slope or in a conservation area.
• Shed dormer: a single flat plane with a shallow slope, simple and efficient.

Do you need planning permission?

Many rear dormers on houses in England can be built under permitted development rights, which currently allow up to 40 cubic metres of additional roof space for terraced houses and 50 cubic metres for semi detached and detached houses, subject to conditions. Dormers cannot face the road under permitted development, must not rise above the highest part of the roof, and should use similar materials. Permitted development does not apply to flats and maisonettes, is restricted in conservation areas and can be removed by an Article 4 direction, which is common in parts of London. Many homeowners apply for a lawful development certificate to confirm the dormer is permitted before building.

What is involved in the build

1. Structural design, including new floor joists and steel beams to carry the dormer.
2. Building regulations approval covering structure, fire safety, insulation and the stairs.
3. Party wall notices for terraced and semi detached homes, because the work usually affects the shared wall.
4. Scaffolding, then opening the roof and building the dormer frame, usually with the house protected from the weather throughout.
5. Insulation, windows, roof lights, a new staircase and fire protected escape route.
6. First fix, plastering, second fix and finishes.

How long it takes

A typical rear dormer takes several weeks on site once approvals are in place, depending on size, the bathroom specification and access. Most of the noisy structural work happens from scaffolding, so many families stay at home through much of it.

How we handle dormer loft conversions on London’s Prestige projects

We manage the whole conversion: design coordination, the structural engineer, permitted development or planning, building regulations, party wall notices, scaffolding and the build itself, with one project manager keeping you updated throughout. Inside, we finish lofts to the same standard as the rest of the house, with fitted storage built into the eaves. See the rear dormer on our Highbury Terrace Mews project, explore our loft conversion service, or read our comparison of a loft conversion versus an extension. Then book a site visit and we will tell you what your roof can take.