House Extensions Streatham
Single storey rear and double storey extensions in Streatham, 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 plans and builds extensions across Streatham, adapting the bay-fronted Victorian and Edwardian terraces of SW16 for modern family living. We handle everything from the side-return infill to the double-storey rear, taking your project from groundworks through steelwork to full fit-out.
In Streatham, 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 Streatham: 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 Streatham
Streatham range: choose above
Side-return and rear extensions in Streatham
The most popular Streatham extension is a kitchen extension that fills in the side return, the narrow strip beside the rear closet wing, and pushes out to the rear to create a wide open-plan kitchen-diner. Because the original rear wall carries the floors and roof above, we install a steel beam sized by the engineer and infill the side return with a glazed roof or lantern to bring light deep into the plan.
We start with the groundworks, digging and pouring foundations to the depth building control requires, mindful of nearby trees and the clay subsoil common across South London. From there we build the walls, set the steel, close in the roof and complete the fit-out, keeping the works tidy while you live around them in your SW16 home.
Housing in Streatham
Count the homes in Streatham and you get about 27,640: 29% built since 1945, 27% between the wars and 43% before 1919, with flats at 67% and houses at 33%. Most homes here are flats, and a flat in Streatham has no householder permitted development rights, so extending one needs planning permission and the freeholder's consent.
Side infills on Streatham terraces after the 2024 boundary change
21% of Streatham homes are terraced houses, and for one with a rear return the Lambeth Local Plan sets a clear steer: infill extensions alongside closet extensions or rear returns should generally be single storey on heritage assets. A house inside the Streatham High Road and Streatham Hill conservation area can fall within that description, and the area's boundary changed in January 2024. An address that was outside it when a neighbour extended may be inside it now, so copying the house next door's two storey infill is not a safe starting point. Check the current map, then design the infill at one storey. Inside a conservation area a side infill is not permitted development, so it needs planning permission whatever its height.
Lambeth's building control charges separate a single storey domestic extension up to 40m2 from a two storey one, and both cover either the building notice or the full plans route. For a Streatham extension we recommend full plans, submitted at least five weeks before starting on site as Lambeth suggests, because approved drawings give the groundworker, the steel fabricator and the neighbour's party wall surveyor the same set to work from. Where planning is needed, a householder application should get a response in 8 weeks, and the full plans set can be prepared while it runs, so the two approvals overlap rather than run end to end.
Planning and permitted development in Streatham
Many single-storey rear extensions on Streatham terraces fall under permitted development, meaning no full planning application is needed, though we always check for an Article 4 direction before relying on it, and in a conservation area side extensions and two-storey additions lose permitted development. Larger schemes, double-storey rears and wrap-arounds usually need a full planning application to Lambeth Council, and we coordinate the drawings and application with your architect or designer.
Whether the route is permitted development or planning permission, the structural work always needs building regulations approval and sign-off, which is separate from planning. Where the extension sits against or excavates near a party wall, you serve notices under the Party Wall Act as building owner, and we give you the drawings they need. We map out every consent your specific SW16 property needs so there are no surprises once the build is underway.
Kitchen extensions in Streatham
67% of homes in Streatham are flats, and a flat has no householder permitted development, so a ground-floor flat's kitchen extension needs planning permission from Lambeth Council and the freeholder's consent. Most kitchen extensions here are on the 33% of homes that are houses. The fit-out is priced on its own page, kitchen renovation in Streatham; the build figures are in the table above.
Double storey extensions in Streatham
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 Streatham often needs planning permission from Lambeth Council. It is a job for the 33% of homes that are houses; a flat cannot add a storey this way. Lambeth's Article 4 Direction withdrawing the Class L(b) right to change a dwellinghouse to a small HMO in Streatham Common and Vale and Streatham St Leonard's wards came into force on 11 August 2025 (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
- Steel goalpost frames where the rear wall opens up
- Drainage diversion and build-over agreements with the water authority
VOA Council Tax stock of properties, March 2025, for all 7 statistical areas in Streatham. Counts rounded by the VOA.
Why Choose GS Renovation in Streatham
Streatham homeowners choose GS Renovation because one team runs the whole extension, from foundations and steel to roofing and the final finish. We advise honestly on whether your scheme is permitted development or needs a Lambeth planning application, handle building control and plan around the party wall notices you serve, and draw on our founder's 30+ years of building.
- Foundation depth set after trial holes, drains and trees are checked
- One point of contact on the phone, not a call centre
- Building control inspected at foundation, damp course and steel stages
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 Streatham
What should I budget for house extensions in Streatham?
Budget for house extensions in Streatham as three amounts inside £2,000 to £2,800 per m² for a rear extension (indicative): the structural element, the finishing trades and the approvals. Approvals belong in the budget wherever the job includes building regulations approval from foundations to completion. GS Renovation lays the SW16 quotation out the same way, so each element can be checked or deferred.
Will my Streatham rear extension need planning permission or is it permitted development?
Many single-storey rear extensions on Streatham terraces are permitted development unless an Article 4 direction removes it, while larger, double-storey or wrap-around schemes, and side extensions in conservation areas, usually need a full application to Lambeth Council. We check your SW16 address first, then advise the correct route. Either way, the structure needs separate building regulations sign-off.
Can I extend my ground-floor flat in Streatham?
Possibly, though not under permitted development, which applies only to houses. A ground-floor flat extension in Streatham needs full planning permission from Lambeth Council, the freeholder's consent under the lease, and often agreement from the flats above, whose windows and drainage may be affected. Building regulations then apply as for any extension. Checking the lease first saves paying for drawings that cannot proceed.
Does the clay under Streatham affect extension foundations?
Yes. The clay subsoil common across South London shrinks and swells with moisture, especially near trees, so building control sets foundation depths to suit the ground found in the trenches. Deeper trenches or a piled solution may be needed. Before the design is fixed, a trial hole in the footprint shows the soil and any old drains, reducing the chance of surprises.
What happens to a drain inside the footprint of my Streatham extension?
It is either moved or built over with the right consent. Part H requires the new drainage to keep proper falls, and a manhole inside the extension may need a sealed cover or relocating. If the pipe is a shared sewer serving other houses, building over it needs the water company's consent before work. A camera survey early on identifies which applies in your SW16 house.
Can my Streatham extension have a flat roof with a lantern?
Yes, and it suits a deep terrace plan by bringing light into the middle of the house. A lantern sits on an upstand on the flat roof, which is built to current insulation standards, and its glazing counts toward the building's heat loss. The roof also needs falls and outlets for rainwater. Rooflights and lantern are sized at design stage.
Could a Lambeth Article 4 Direction restrict a Streatham extension that would otherwise be permitted development?
Lambeth names nine conservation areas, in all or part, as having Article 4 Directions on external alterations, and Streatham Lodge and Leigham Court Estate are among them alongside Albert Square, Hyde Farm and Vauxhall. Where a direction applies, work that would otherwise be permitted development can need a planning application. Check your Streatham address against that list before relying on permitted development, and read the direction for your area, since they differ in what they cover.
Does a post-war Streatham house extend differently from a period one?
In the detail, yes. 29% of Streatham homes were built after 1945, and houses of that age can have cavity walls and solid ground floors, so the new extension ties into a cavity and its damp proof course lines up with a modern one. Drainage can be the bigger constraint: post-war layouts can have shared private drains running across rear gardens, and building over one needs agreement from the water company before the foundations are dug.
Is pre-application advice worth it for a Streatham extension in a conservation area?
Lambeth's householder pre-application fee is higher for a house or flat in a conservation area or a locally listed or listed building than for one outside, but the written advice lets you test a design before paying for full drawings. For an extension inside the Streatham Common conservation area, ask about depth, roof form and materials, and bring photographs of approved extensions on neighbouring houses to support the case.
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