House Extensions Clapham
Single storey rear and double storey extensions in Clapham, planning, structure and build under one contract.
- Rated 4.9 from 31 reviews on MyBuilder
- Single-storey rear extension from £40,000
- Free site survey, itemised quote
GS Renovation builds extensions across Clapham, working on the bay-fronted Victorian and Edwardian terraced houses of SW4. We handle rear, side-return and wrap-around kitchen extensions from foundations and steelwork through to a full fit-out, keeping the works tidy in your occupied home.
In Clapham, a single-storey rear extension typically starts from £40,000, or £2,000 to £2,800 per m² (indicative London ranges, Architecture for London, Resi, MyBuilder and Checkatrade, 2026). GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Clapham: the structural engineer we appoint designs the structure, we build it, and building control signs it off.
Price guide
| Work | Indicative London range |
|---|---|
| Single-storey rear extension | from £40,000 |
| Rear extension, per m² | £2,000 to £2,800 |
| Side return, per m² | £2,400 to £3,200 |
| Wraparound, per m² | £2,400 to £3,200 |
| Double storey, per m² | £1,800 to £2,600 |
| Basement extension | see the basement page |
Indicative London ranges (Architecture for London, Resi, MyBuilder and Checkatrade, 2026), not a quotation. Prices checked September 2026. Full breakdown: Extension Costs & Planning.
Quick estimate for Clapham
Clapham range: choose above
Side return and rear extensions in Clapham
The classic Clapham extension fills in the side return beside the rear closet wing, capturing the narrow strip of yard that most SW4 terraces waste. Combined with a rear extension, this creates the wide, open kitchen-diner that suits family life near the Common. We dig new foundations to suit the ground, build the walls, and install steel beams to carry the existing structure over the enlarged opening.
Because these terraces sit wall to wall with their neighbours, extensions almost always involve the Party Wall Act, whether you are building along the boundary or excavating near the adjoining foundations. You serve the notices as building owner (or your surveyor does); we give you the drawings the notices need, work to any award the surveyors agree, and sequence the groundworks so your neighbour's wall stays supported throughout the build.
Housing in Clapham
The stock in Clapham runs to roughly 22,800 dwellings, 72% of them flats and 28% houses, built 58% before 1919, 6% between 1919 and 1939 and 34% after 1945. Since most homes here are flats, a flat in Clapham has no householder permitted development rights, so extending one needs planning permission and the freeholder's consent.
Side infills beside Clapham closet wings and the single storey steer
The Lambeth Local Plan policy on building alterations and extensions says infill extensions alongside closet extensions or rear returns should generally be single storey on heritage assets. In Clapham, where 58% of homes were built before 1919 and the Clapham conservation area is centred on the Common, that sentence shapes the brief early. For a house that counts as a heritage asset, plan the side infill as a single storey and look for any extra first floor space elsewhere, or accept a harder planning case. Finding out whether your house counts is the first job, since designation, not age alone, decides it.
Lambeth's building control fee guide treats a single storey domestic extension up to 40m2 separately from a two storey one of the same size, and each is a total charge covering the building notice or full plans route. Knowing which band a Clapham scheme falls in helps when comparing quotes, because some include building control and some leave it to you. Pre-application advice costs more for a house or flat in a conservation area than for one outside. For a house near the Common, make it count with one clear question to Lambeth: can the infill and the rear extension be read as one single storey addition.
Permitted development or planning in Lambeth and Wandsworth
Some Clapham extensions fall under permitted development, but many do not. A single-storey rear extension within the size limits can still be permitted development in a conservation area, unless an Article 4 direction removes it, but a side-return infill counts as a side extension there and needs planning permission, as do two-storey extensions. Flats have no householder permitted development at all. Clapham straddles two boroughs: most of SW4 is Lambeth, but the streets on the west side of the Common towards Clapham Junction are in Wandsworth, so we confirm which council covers your address first. We assess your specific SW4 house before design so you know which route applies rather than assuming.
Once the planning position is settled, the structural side is governed by building regulations, with building control inspecting the foundations, steelwork, insulation and drainage. We manage both threads together, then complete the roof works, glazing, plastering, electrics and plumbing, handing back a finished room rather than a shell for another trade to fit out.
Kitchen extensions in Clapham
72% of homes in Clapham are flats, and a flat has no householder permitted development, so a ground-floor flat's kitchen extension needs planning permission from Lambeth Council or Wandsworth Council and the freeholder's consent. Most kitchen extensions here are on the 28% of homes that are houses. The fit-out is priced on its own page, kitchen renovation in Clapham; the build figures are in the table above.
Double storey extensions in Clapham
Under permitted development a two-storey rear extension can go no more than 3 metres beyond the original rear wall and must stay at least 7 metres from the rear boundary, and in a conservation area it is not permitted development at all. Many gardens are too short for the 7 metre rule, so a double storey extension in Clapham often needs planning permission from Lambeth Council or Wandsworth Council. It is a job for the 28% of homes that are houses; a flat cannot add a storey this way. Lambeth's Clapham conservation area (CA 01), first designated in 1968, is centred on Clapham Common (council source). Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.
- Side-return and rear extensions
- Drainage diversion and build-over agreements with the water authority
- Insulation, airtightness and thermal detailing to regulations
VOA Council Tax stock of properties, March 2025, for all 6 statistical areas in Clapham. Counts rounded by the VOA.
Why Clapham Homeowners Choose GS Renovation
Clapham homeowners choose GS Renovation because we run the whole extension under one roof, from the first foundation to the final coat of paint. We know how SW4 terraces are built, we coordinate the work around the party wall award and the planning position honestly, and our founder's 30+ years on the tools mean the steel, the groundworks and the finish all come from one accountable team.
- Site left safe and secure at the end of every day
- Drainage diverted or built over with the right approval in place
- Permitted development checked before you pay for a planning application
Built a new extension at rear of property. Laid foundations, drainage, raised floor, new roof and completed all fixtures and interior decoration…
George was brilliant. Lovely bloke, very reasonably priced and a perfectionist to boot. He completed our small kitchen renovation with care and great…
George always kept to commitments and arrived on time. He offered helpful suggestions during his initial visit and promptly provided a reasonably…
FAQ
Frequently Asked Questions about House Extensions Clapham
How does your house extensions price in Clapham compare with a national firm's?
Against a national firm, a GS Renovation quotation for house extensions in Clapham is more transparent: every line within £2,000 to £2,800 per m² for a rear extension (indicative) is visible, including the engineer's design and the Lambeth Council or Wandsworth Council building control fee. National pricing tends to be a rate per square metre for an SW4 address nobody has visited, which misses that the drainage run under the footprint decides the foundations.
Will my Clapham extension need planning permission from Lambeth Council?
A single-storey rear extension is often permitted development, but in a conservation area a side-return infill needs planning permission, and so does any extension where an Article 4 direction has removed the rights. The application goes to Lambeth Council for most of SW4, or to Wandsworth Council for homes on the west side of the Common. We check your specific SW4 home first, then handle the application if one is required and the building regulations sign-off either way.
Who has to agree to an extension on a Clapham ground-floor flat?
The freeholder, in writing, and the council through a planning application, Lambeth for most of Clapham or Wandsworth west of the Common, because flats have no permitted development rights. Owners of the flats above may also be affected where the extension ties into shared walls. Building regulations approval follows regardless. Settle these before paying for detailed design.
What happens to the drains in a Clapham side return when it is built over?
The gully, rainwater pipe and any soil pipe in a house's side return are usually relocated, and any manhole under the footprint is rebuilt or moved. If the run is a shared or public sewer, building over or near it needs the water company's consent. Part H sets the falls for the new pipes.
How does rain get off a side return extension roof along a Clapham boundary?
Usually through a box gutter or a parapet gutter running along the boundary wall, falling to a downpipe at one end. The gutter must not hang over the neighbour's side, and it needs enough fall and capacity for a heavy storm. It connects to the drains under Part H.
Where does the new steel bear in a wrap-around extension on a Clapham terrace house?
Mainly at one corner. In a house where both the rear wall and the side wall of the closet wing come out, that corner becomes a point load, usually carried by a steel post on its own pad foundation. The engineer sizes the post and pad, and building control inspects the foundation first.
Is the Clapham conservation area among Lambeth's Article 4 areas for external alterations?
Lambeth lists all or parts of Albert Square, Hyde Farm, Lansdowne Garden, Leigham Court Estate, Park Hall Road, St Marks, Stockwell Park, Streatham Lodge and Vauxhall conservation areas as having Article 4 Directions on external alterations. The Clapham conservation area is not one of those names. Inside it, a single storey rear extension within permitted development limits may still be possible, but a side infill or a two storey rear extension needs planning permission. A flat has no householder permitted development at all. Check your exact address, as a street near a boundary could fall within a different area.
How long should a Clapham extension programme allow for a householder planning decision?
A response to a householder application should come in 8 weeks, according to Lambeth, and pre-application advice taken beforehand adds its own time. For a Clapham house the sequence we plan is advice, application, decision, and then party wall notices served by you as building owner, so the neighbour's surveyor sees the approved drawings rather than a draft that may still change. Groundworks are booked only once the decision is in hand.
Can a Clapham house take a two storey rear extension instead of a side infill?
Sometimes, though it is a different planning case. Inside the Clapham conservation area a two storey rear extension falls outside permitted development, so it needs planning permission. Lambeth's steer that infills beside closet extensions should generally be single storey on heritage assets applies to the infill, not the rear extension, and building control charges a two storey domestic extension up to 40m2 as its own band. On a Clapham terrace, test light to the neighbours' rear windows first, ideally through pre-application advice before drawings are finished.
Every Service, One Team
More GS Renovation Services in Clapham
One team for every GS Renovation service in Clapham:
Same Service, Nearby Areas
House Extensions Near Clapham
We carry out house extensions across Clapham and the surrounding areas. Explore a nearby location:
Ready to Start Your Clapham Project?
Free, no-obligation quote for house extensions in Clapham.