House Extensions Southwark
Single storey rear and double storey extensions in Southwark, 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 house extensions across Southwark, where most homes are flats, adding space to Victorian terraces in Peckham, Georgian townhouses in Dulwich and family homes in Camberwell. We handle groundworks, steel, roofing and fit-out, and we guide you through permitted development and Southwark Council planning.
In Southwark, 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 Southwark: 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 Southwark
Southwark range: choose above
Side return and rear extensions in Southwark
On a Southwark Victorian terrace, the usual extension fills in the side return, widening a narrow rear kitchen into a full-width, open-plan space. This nearly always needs a steel beam where the original rear wall comes down, sized by a structural engineer and signed off by building control. We dig and pour new foundations to the correct depth, allowing for nearby trees on plots close to Peckham Rye, and tie the new structure into the existing brickwork.
Whether your extension is permitted development or needs a full planning application depends on the property. A modest single storey rear extension on a Peckham or Bermondsey house may fall under permitted development, and can still do so in a conservation area unless an Article 4 direction removes it. Side and two-storey extensions in a conservation area need planning permission from Southwark Council, and a listed home, as many Dulwich and Camberwell properties are, needs listed building consent as well. We assess this early and tell you which route applies before design money is spent.
Housing in Southwark
For Southwark the Council Tax list gives about 149,990 homes; by type 81% flats and 19% houses, by age 64% post-war, 7% interwar and 25% older than 1919. Since most homes here are flats, a flat in Southwark has no householder permitted development rights, so extending one needs planning permission and the freeholder's consent.
Southwark's rear extension rules, and Camberwell Green's one storey limit
Southwark's Cabinet decided to adopt the Householder Development Supplementary Planning Document at its meeting of 07/07/2025. The SPD says a single storey rear extension without planning permission is not available to flats, maisonettes, homes in a Conservation Area or listed homes. Where a house does qualify, it says a terraced or semi-detached home can be extended to the rear by up to 3m in depth with a maximum height of 4m. For a flat or a listed home, that means an application. For a house in a conservation area, the national permitted development rules are the test, and they still allow a single storey rear extension unless a direction has removed that right. Settle it with a lawful development certificate from Southwark before paying for a design.
Conservation area appraisals then add local limits. Southwark's Camberwell Green Conservation Area was originally designated in February 1981, and its appraisal says rear extensions should normally be no more than one storey in height. A two storey rear addition there starts from a presumption against it, so a single storey scheme with a better plan is the safer starting point. For the structure, a single storey extension also means lighter foundations and one steel over the opening, which the structural engineer we appoint can size once the planning drawings are settled.
Double storey extensions across Dulwich and Peckham
Where the plot allows, we build double storey and wrap-around extensions that add a bigger kitchen below and an extra bedroom or bathroom above. These are common on the larger Georgian and Edwardian homes around Dulwich Park and the leafier streets of SE21 and SE22. They need deeper foundations, more substantial steelwork and careful integration of the new roof with the old. Almost all double storey extensions in Southwark require planning permission rather than permitted development.
Because Southwark plots sit close together, extensions frequently trigger the Party Wall Act where you build up to or astride a boundary, or excavate near a neighbour's foundations. You serve the notices as building owner (or your surveyor does) and keep neighbours informed; we supply the drawings and build to any award. Once the shell is watertight, the same team completes the fit-out: plastering, electrics, plumbing, flooring, heating and decoration, so you deal with one contractor from the first trench to the final coat of paint.
Kitchen extensions in Southwark
81% of homes in Southwark are flats, and a flat has no householder permitted development, so a ground-floor flat's kitchen extension needs planning permission from Southwark Council and the freeholder's consent. Most kitchen extensions here are on the 19% of homes that are houses. The fit-out is priced on its own page, kitchen renovation in Southwark; the build figures are in the table above.
- Roof works and structural alterations at roof level
- Building control inspections at foundation, damp course and steel stages
- Flat and pitched roofs with rooflights or lanterns
VOA Council Tax stock of properties, March 2025, for all 34 statistical areas in Southwark. Counts rounded by the VOA.
The GS Renovation Difference in Southwark
Homeowners in Southwark choose GS Renovation because we run the whole extension in-house, from foundations and steel to roofing and finishes, across SE1 to SE22. We know the borough's period houses, its tight terraced plots and its conservation constraints, and we keep the Southwark Council planning and building control steps in order so your project stays on track and fully compliant.
- Foundation depth set after trial holes, drains and trees are checked
- Building control applications and inspections coordinated for you
- Brick and mortar matched to the existing elevation
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 Southwark
What is the going rate for house extensions around Southwark?
House extensions around Southwark typically costs £2,000 to £2,800 per m² for a rear extension (indicative), but scope varies more than the market does. Two Southwark jobs of the same size can be different work, because the drainage run under the footprint decides the foundations. GS Renovation surveys and prices each on its merits at SE1, with the Southwark Council building control fee shown separately.
Do I need planning permission for a rear extension in Dulwich?
Much of Dulwich falls within conservation areas and includes listed buildings, where permitted development rights are restricted. A modest single storey rear extension can still be permitted development in a conservation area unless an Article 4 direction removes it, but a listed house needs listed building consent, and side, two-storey and larger schemes need planning permission from Southwark Council. We check your address and constraints at the outset and tell you which route applies before design money is spent.
Can a Southwark flat be extended?
Sometimes, but never under permitted development, because those rights belong to houses and exclude flats and maisonettes entirely. Extending a flat means applying to Southwark Council for planning permission, securing the freeholder's agreement under the lease and gaining Building Regulations approval. Flats make up 81% of Southwark's housing in the VOA data, so that is the normal path here.
How do trees near Peckham Rye affect a Southwark extension's foundations?
Tree roots dry the soil in summer and let it swell in winter, so foundations near them must go deeper than usual. On plots close to Peckham Rye or with mature garden trees, the engineer sets foundation depth by the tree's species and distance and may specify heave protection. Check whether the tree is protected before any roots are cut.
How does a double storey extension in Southwark join the existing house?
Through deeper foundations, heavier steel and a new roof tied into the old one. The rear wall is propped and opened on engineer-sized beams at both levels, and the new walls are toothed into the existing brickwork. Double storey schemes in Southwark almost always need planning permission, and building control inspects each stage.
Do my neighbours need notice when I dig foundations for a Southwark extension?
Usually, yes. If your trench runs within 3 metres of the house next door and goes deeper than its footings, the Party Wall Act asks for one month's written warning before digging starts. Your neighbour may agree in writing or dissent, and dissent means surveyors agree an award. Put that month into the programme before booking the excavator.
How much of a Southwark garden can a rear extension take?
Southwark's Householder SPD says rear extensions must not take up more than 50% of the total rear garden space. On a short plot that limit can bite before any depth limit, particularly when a side infill and a rear section are combined. Measure the garden as it is now, ask how any existing rear addition is counted, and ask the designer to state the garden left over as a figure on the drawings so the test is visible when the application is read.
Does a Southwark rear extension pay the Community Infrastructure Levy?
Rarely, but it has to be handled properly. Southwark's draft revised CIL charging schedule lists extensions to buildings of less than 100 square metres as exempt, unless the development will comprise one or more dwellings, which means creating a new home. Where CIL does apply, Southwark's schedule sets residential rates across Zones 1, 2 and 3, and Southwark also collects the Mayor of London's CIL on top of the borough rates. A larger extension to your own home can also be exempt, but that relief has to be claimed before work starts.
How is Southwark's building control charge for an extension worked out?
By floor area bands. Southwark's final fees and charges schedule sets one charge for an extension less than 40sqm and another for an extension between 40 and 60sqm. The schedule also shows the smaller band's charge has gone up from its previous level. Take the internal floor area from the drawings, not an estimate, and if the scheme sits just over the 40sqm line, see whether a small trim moves it into the lower band.
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