House Extensions Balham
Single storey rear and double storey extensions in Balham, 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 Balham, working with the bay-fronted Victorian and Edwardian terraces that define SW12. Side-return infills, kitchen extensions and rear extensions are the usual projects here. We take a Balham extension from foundations and steelwork through to a fully fitted, building control signed-off finish.
In Balham, 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 Balham: 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 Balham
Balham range: choose above
Side-return extensions on Balham terraces
Balham's terraces almost all have a narrow side return running alongside the rear closet wing, and infilling it is the classic way to widen a cramped kitchen into a bright kitchen-diner. We dig and pour the foundations, tie the new structure into the existing solid brick wall, install the steel beams that carry the original rear wall and build up with a mix of solid roof and rooflights to pull daylight deep into the plan.
A single-storey rear or wrap-around extension on these plots often falls under permitted development, but not always. Conservation area status, previous additions, the closet wing and how close you build to the boundary can all tip a project into needing a full planning application to Wandsworth Council. We assess your specific house early, advise honestly on which route applies and prepare the drawings either way so there are no surprises.
Housing in Balham
The valuation list shows roughly 7,240 homes in Balham, of which 68% are pre-1919, 8% interwar and 24% post-1945, split 55% flats to 45% houses. Most homes here are flats, and a flat in Balham has no householder permitted development rights, so extending one needs planning permission and the freeholder's consent.
Rear and side extensions in Balham's conservation areas
In a Wandsworth conservation area, the council's FAQ lists front and side extensions of one storey or more, and two storey rear extensions, among works that need planning permission. Balham has more than one such area. The council's appraisal places the Nightingale Lane Conservation Area within Balham, SW12, and the Old Devonshire Road Conservation Area covers the first area in Balham to be developed away from Balham High Road, in the early 19th century. For a terrace inside either, a side return infill counts as a side extension, so it goes in as a planning application. A single storey rear extension within the permitted development limits is not on that list.
The Old Devonshire Road Conservation Area appraisal adds a point for anything above the ground floor. It says roof extensions and dormer windows are not a common feature of the area and exist only where part of the original design of the building. A scheme there that adds a dormer or roof extension alongside a rear extension runs against that sentence, so keep the new roof forms simple. Outside the conservation areas, a terraced house, the type that makes up 37% of Balham's homes, can often extend at the rear under permitted development, and the drawings test its limits and the neighbours' light before anything is built.
Double-storey extensions in SW12 homes
Where a family needs a bedroom and bathroom as well as more ground-floor space, a double-storey rear extension over the closet wing is the bigger option for a Balham terrace. This is bigger structural work, with heavier steel, deeper foundations and a roof that must marry into the existing Victorian roofline, so it almost always requires planning permission from Wandsworth Council rather than falling under permitted development.
Because the flank and rear walls are usually shared with neighbours, party wall notices come into play alongside the building regulations that govern the structure, insulation, drainage and fire safety. You serve those notices as building owner, and we give you the drawings and programme they need. We manage the rest of the chain: engineer, planning drawings, groundworks, steel, roofing and the full internal fit-out. One accountable team means the Balham extension is delivered to a single standard, on a single programme, from first dig to final decoration.
Kitchen extensions in Balham
55% of homes in Balham are flats, and a flat has no householder permitted development, so a ground-floor flat's kitchen extension needs planning permission from Wandsworth Council and the freeholder's consent. Most kitchen extensions here are on the 45% of homes that are houses. The fit-out is priced on its own page, kitchen renovation in Balham; the build figures are in the table above.
- First fix and second fix plumbing and electrics throughout
- Brickwork and mortar matched to the existing elevation
- Party wall process explained, and the extension built to the award
VOA Council Tax stock of properties, March 2025, for Balham and Nightingale Lane. Counts rounded by the VOA.
The GS Renovation Difference in Balham
Balham families choose GS Renovation because we understand exactly how these terraces are built, from the side return to the closet wing to the shared party walls. We advise clearly on permitted development versus a Wandsworth planning application, handle foundations, steel, roofing and fit-out under one roof, and back every job with building control sign-off and our founder's 30+ years of experience.
- Building control inspected at foundation, damp course and steel stages
- Foundation depth set after trial holes, drains and trees are checked
- A written scope and programme agreed before work starts
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 Balham
Is the price of house extensions higher in Balham than elsewhere in South West London?
Work on house extensions in Balham is priced from scope, so it costs no more than the same house in Streatham, typically £2,000 to £2,800 per m² for a rear extension (indicative). Costs rise in period stock and with awkward access, both checked at SW12. What neither changes is the order of work: drainage under the footprint is diverted before foundations are poured. GS Renovation shows each as its own line.
Does my Balham side-return extension need planning permission?
Many single-storey rear and side-return extensions in Balham qualify as permitted development, but conservation area status, earlier additions or building close to the boundary can require a full planning application to Wandsworth Council. Double-storey extensions almost always need permission. We assess your specific property first and prepare the right drawings, plus the building regulations submission, whichever route applies.
Can the owner of a ground floor Balham flat extend at the back?
It is possible, but flats have no permitted development rights, so a rear extension to a ground floor flat needs full planning permission from Wandsworth Council. With flats making up over half of Balham homes, this catches many owners out. The lease will also need the freeholder's written consent, and where the upstairs flat owns a share of the freehold, those owners are usually party to that consent too.
What happens if a sewer runs under the site of my Balham extension?
The drainage route is established before the footprint is fixed. Terraces often share a run of drainage across the back of several houses, and where one of those runs is a public sewer, the water company has to agree before a footing is poured over or beside it. A drainage survey with a camera shows where the pipes run. Shifting the footprint on paper is easier than after digging.
How do you stop the middle of a Balham house going dark after an extension?
By bringing light down where the old rear wall used to be. Once a Balham house is extended, the original back room sits in the middle of the plan, so a rooflight or roof lantern is placed as close to that junction as the structure allows. The steel carrying the old rear wall is designed with the rooflight position in mind. Part L insulation standards then decide how much glazing the new roof can take.
What does building control check during a Balham extension?
Inspections follow the build stages. The inspector sees the foundation trenches before concrete is poured, the drainage before it is backfilled, the damp proof course and then the steel and insulation before they are covered. Building regulations apply to every extension regardless of the planning route, and Wandsworth Council issues a completion certificate at the end.
How are Wandsworth building control charges set for a Balham extension up to 40 square metres?
They are fixed, by floor area. Wandsworth Building Control has fixed charges for an extension with an aggregate floor area of up to 40 square metres, either as a plan charge plus an inspection charge or as a single building notice charge, including VAT. Aggregate means every new room added together, so a Balham side return infill and a rear extension built at once count as one total.
Is a paid pre-application meeting worth it for a Balham side return in a conservation area?
For a scheme on the list of works needing permission, it is worth weighing up. Wandsworth's householder pre-application fees for 2026/2027 cover a meeting and written advice, or a meeting only of up to 1 hour. In a Balham conservation area the written advice is the version to choose, because it can be referred to in the application and shows the design responded to the officer's comments.
Can a Balham extension start on site under a building notice?
It can. With a Wandsworth building notice you can start work 48 hours after the notice is submitted, provided the correct fee has been paid, and the notice is invalid until it is. For an extension with foundations and steel, full plans is usually the better route, because the drawings are checked before the digger arrives and the charge is split between application and the first site visit. A building notice also cannot be used where the extension is built over or near a public sewer.
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