GS Renovation converts lofts in Clapham, on the handsome Victorian terraces that run back from Clapham Common through SW4. Conservation area coverage is heavy here, which pushes a lot of schemes towards a mansard rather than a rear dormer. We coordinate the engineer, build the structure and manage Lambeth Council building control.
Dormer or mansard on an SW4 terrace
On an unconstrained Clapham terrace, the standard answer is a rear dormer, or an L-shaped dormer where the house retains its closet wing. Both give you a double bedroom and usually an en suite, and both rely on steel beams spanning between the party walls to carry a new floor and the dormer above. Indicative London ranges for 2026 are roughly £45,000 to £65,000 for a rear dormer and £55,000 to £80,000 for the L shape.
Many of the streets around Clapham Common sit within Lambeth conservation areas, and there a boxy rear dormer is likely to be refused. A mansard is often the form that gets consent, because its steep front slope and setback read as part of the original roof rather than an addition. It is the most expensive route, indicatively £70,000 to £100,000 or more, but it also delivers the most usable volume.
Head height, structure and Lambeth consents
We start at the ridge. If you have roughly 2.2m to 2.4m from the top of the ceiling joists to the underside of the ridge, the loft converts inside the existing roof. Victorian roofs in SW4 usually do, but a house that has been re-roofed with heavier tiles, or one with a shallow pitch over a later rear addition, can be tighter than it looks from the street. The tape measure settles it, not the estate agent's floorplan.
Conservation area designation removes permitted development rights, so a planning application to Lambeth Council is needed rather than a lawful development certificate. Building regulations apply either way: a protected stair route with fire doors and interlinked alarms under Part B, stair geometry and headroom under Part K, engineer-designed floor joists off new steels, and insulation and ventilation to Part L. We book the inspections and hold the paperwork.
- New floor joists independent of the existing ceiling
- Staircase design to Part K, including the landing below
- Trussed roofs redesigned before any web is cut
- Rear dormers to win full head height across the new floor
- L-shaped dormers over a rear closet wing
Trusted Loft Conversion in Clapham
Clapham owners use GS Renovation because SW4 lofts are rarely simple: shared party walls on both sides, conservation constraints and tight street access all have to be planned around. We coordinate the engineer and architect, install the steelwork, build the stair and fire strategy properly and take the job through Lambeth Council building control. Fully insured, with a dedicated project manager on every project.
- Staircase set out to Part K within the space you have
- Founder-led team with 30+ years of hands-on experience
- Straight advice on what is and is not worth spending money on
- One point of contact on the phone, not a call centre
- Protected stair route and fire doors detailed to Part B
- Waste cleared as we go, not left piled in the garden