Dormer Loft Conversion London — Planning, Cost & What to Expect

What is a Dormer Loft Conversion?

A dormer is a box-shaped structure that projects vertically from an existing sloping roof. By adding a vertical rear wall and a flat (or near-flat) roof to part of the existing roof slope, it creates significantly more usable headroom and floor area than a simple rooflight conversion.

Rear dormers are the dominant loft conversion type in London's Victorian and Edwardian terraces — they are efficient, cost-effective, and clearly understood by Planning Authorities.

Does a Dormer Need Planning Permission?

In most cases: no. A rear dormer on a terraced, semi-detached or detached house typically falls within Permitted Development (PD) rights, provided:

- The volume added does not exceed 50m³ (40m³ for terraced houses) - The dormer does not extend above the existing roof ridge - The dormer does not face a highway (front dormers require full planning) - Your property is not in a Conservation Area or subject to Article 4 Direction

Many inner London boroughs (Islington, Hackney, Southwark, Lambeth, Hammersmith & Fulham) have removed PD rights for extensions and loft work via Article 4 Directions. Always check with your local planning authority before assuming PD applies.

The Building Process

Week 1–2: Scaffold erected (typically wrap around scaffold to give safe access to rear roof). Structural calculations produced and Building Control application submitted.

Week 2–4: Existing roof opened — rafters cut, steelwork installed (typically Flitch beams or RSJs), new floor joists installed and strengthened.

Week 4–6: Dormer structure built, flat roof installed (GRP or standing seam zinc), windows glazed, roof made watertight.

Week 6–9: First fix electrics and plumbing (en-suite), insulation, plasterboard, new stair installed.

Week 9–12: Plastering, second fix plumbing and electrics, tiling, flooring, decoration, stair balustrade installation, Building Control sign-off.

What is Included in SuperBuilder's Dormer Package

Our dormer packages include full structural design and engineering, Building Control application and sign-off, Party Wall notices and Awards through our surveyor network, all scaffolding, a full Velux or equivalent window package, en-suite bathroom, and complete internal decoration.

Call 0800 530 0853 or request a free survey online.