— Clapham Old Town · Abbeville · Clapham Park · SW4

Loft conversions in Clapham.

In Clapham the question isn’t whether you’re in a conservation area. It’s which one — there are four with Clapham in the name, and several more next door.

Lambeth has 62 conservation areas covering roughly 30% of the borough, and SW4 carries a heavy share of them. That single fact changes what your roof can take, how long the process runs and what the job costs. This page tells you how to check your own address in about two minutes — before you pay anyone for drawings.

— The Clapham problem

Four conservation areas called Clapham, and several more next door.

Most South London boroughs have a handful of conservation areas and a homeowner can reasonably guess whether they are in one. Lambeth is not like that. The council’s own figure is 62 conservation areas covering approximately 30% of the borough — close to a one in three chance before you check anything.

In and immediately around Clapham, these are the ones that catch houses:

Boundaries between them run along the backs of gardens and through the middle of terraces. It is entirely normal for one side of a road to sit inside a conservation area and the other side to sit outside it — with the same houses, built by the same developer, in the same year.

This is why “my neighbour got a dormer so I can too” is unreliable advice in Clapham, and why guessing costs people money.

— Check it yourself

How to find out about your own house in two minutes.

Most builders won’t tell you this because they would rather you rang them. We would rather you knew before the first conversation, because it makes that conversation useful.

Lambeth publishes the answer, free, in two places:

• The planning application database. Search for your address, open the result, and click the Constraints tab. If the property sits inside a conservation area, it is listed there — along with anything else affecting the site.
• The council’s conservation area map. An interactive map showing every designated area in the borough, so you can see exactly where the boundary runs relative to your house.

Both are reachable from Lambeth’s conservation area profiles page, which also holds the appraisal document for each area. If you are inside one, read your area’s appraisal — it describes what the council considers special about the street, and that is what any application will be judged against.

Lambeth’s planning team can also be reached on 020 7926 1180. Separately, a small number of Lambeth properties have had permitted development rights removed by an Article 4 direction, or by a condition attached to an earlier planning permission on the site. Both show up on the constraints check.

Renovating rather than just converting? See house renovation in Balham next door.

— What changes if you’re inside one

Inside a conservation area, outside a conservation area.

Outside, a Clapham terrace normally keeps full permitted development rights. That means up to 40 cubic metres of added roof volume on a terraced house, provided nothing projects forward of the roof plane facing the street, nothing rises above the existing ridge, and materials are similar in appearance to the existing house. Side-facing windows must be obscure-glazed and non-opening below 1.7 metres. No planning application needed — though we always recommend a Lawful Development Certificate.

Inside, conservation area designation removes some of those rights nationally, and any scheme has to preserve or enhance the character of the area. In practice, for a Clapham terrace, that usually means:

• Nothing visible from the street. Rear elevations carry the work; front roof slopes stay as they are.
• Rooflights rather than dormers on any visible slope, and conservation-pattern rooflights that sit flush with the tiles rather than standing proud.
• Matched materials. Slate to match slate, and often reclaimed rather than new.
• Set-back dormers. Where a rear dormer is accepted, it is usually required to sit below the ridge and in from the party walls and the eaves rather than filling the whole roof slope.
• A full planning application, with a determination period of around eight weeks.

The practical effect on space is smaller than people fear. A set-back rear dormer on a Clapham terrace still comfortably yields a double bedroom, and where there is a rear addition, an L-shaped dormer adds a bathroom on top of that.

Conservation area information checked against Lambeth Council’s published conservation area profiles in July 2026. Boundaries are redrawn and designations change. Confirm your own address using the constraints check described above, or contact Lambeth Council or the Planning Portal before committing to a design.

— What we build

Types of loft conversion we build in Clapham.

L-shaped dormer

The Clapham standard for a Victorian terrace with a rear addition — two dormers joined over the main roof and the back addition, giving a double bedroom plus a separate bathroom. Invisible from the street, which is what makes it workable inside a conservation area.

Set-back rear dormer

Where there is no rear addition, or where the conservation area appraisal is particularly protective of the rear roofscape. Sits below the ridge and in from the party walls, which reads as a subordinate addition rather than a box on the roof.

Rooflight conversion

No change to the roof shape at all — conservation-pattern rooflights set flush into the existing slope. The least contentious option by a wide margin, and the right answer where the roofscape is tightly controlled or the head height is already generous.

Mansard

Maximum floor area, near-vertical walls. In a conservation area a mansard needs precedent on the street — where neighbouring properties already carry them, the case is straightforward; where the terrace roofline is unbroken, it rarely is. We will tell you which of the two you are looking at on the first visit.

— Building Regulations

Building Regulations apply either way.

Whether or not you need planning permission, every loft conversion needs Building Control approval. Structure under Part A — existing ceiling joists are never adequate as floor joists, so new joists and usually steel beams. Fire safety under Part B — a loft makes a third storey, which triggers a protected escape route, fire doors off the stairwell and interlinked mains-powered alarms on every level. Stairs under Part K, insulation under Part L, ventilation under Part F.

Clapham is terraced, so the Party Wall etc. Act 1996 applies to virtually every job here — usually to both neighbours. Two months’ notice. We manage the process; the surveyor’s fee sits outside our quote.

— Costs

Loft conversion costs in Clapham.

Honest 2026 ranges. Clapham sits above the outer boroughs mainly because of access — permit bays, narrow side returns and no driveway to put a skip on — and because conservation area work means matched materials rather than the cheapest equivalent.

Why these look lower than the London averages you’ll read elsewhere

Published London figures often quote £3,000 to £4,500 per square metre. Ours work out lower, for three reasons and no catch. Those averages are usually Inner London rates — Chelsea and Kensington run well above SW4. They are frequently quoted inclusive of VAT and professional fees, where ours exclude both and say so. And we run a maximum of three projects at a time with our own trades, so there is no management margin stacked on another contractor’s margin.

→ See our full pricing guide for South London renovations

— Why LMDEC

Why Clapham homeowners choose us.

We check the constraints before we quote, not after. Two decades of hands-on experience on South London period homes, and enough Lambeth conservation area work to know that the answer depends on which side of the road you are on. The people who quote your job are the people who build it.

A fixed price in writing, and realistic dates. Every quote itemised before work starts. If the strip-out uncovers something genuinely hidden — and Victorian Clapham hides plenty — you see the cost and the options before anyone continues. A maximum of three projects at a time across the whole company.

£2 million Public Liability insurance, two-year workmanship warranty, six-month return visit included. Wet rooms and tanked floors carry a separate ten-year waterproofing guarantee. All gas work by individually qualified Gas Safe registered engineers; all electrical work by individually qualified NICEIC certified electricians. Building Regulations completion certificate and your guarantee in writing on handover.

Every project includes the Prestige Client Portal at no extra cost. A live schedule, dated site photographs, every drawing and consent in one secure place, and one-click approval of any variation with the cost shown before you decide.

— Common questions

Frequently asked.

Part of our loft conversions across South London — including neighbouring Wandsworth, Dulwich and Croydon. Looking at an extension or full refurbishment instead? We do those too.