House Extensions Deptford
Single storey rear and double storey extensions in Deptford, 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 on Deptford's houses, a minority in an area of post-war flats, from later terraces to SE8's few Georgian townhouses, working to your designer's approved drawings and the structural engineer's calculations. We handle everything from foundations and steel beams to roofing and full fit-out, and we tell you early whether the scheme is likely to be permitted development or need a planning application to Lewisham Council.
In Deptford, 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 Deptford: 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 Deptford
Deptford range: choose above
Rear and side-return extensions in Deptford
On a Deptford house, the usual extension fills in the side return or pushes out the rear to create a bright, open kitchen-diner. We dig and pour foundations to suit the ground and any nearby trees, then build up in brick or blockwork to match the existing property. A steel beam, sized by the engineer, usually carries the original rear wall so the new and old spaces flow together as one room.
Many single storey rear extensions on Deptford houses fall under permitted development, which avoids a full planning application. However, if you plan a larger or double storey addition, or a side extension in a conservation area, you will need planning permission from Lewisham Council, and listed building consent if the townhouse is listed. We assess your specific property early and advise honestly on which route applies before any drawings are finalised.
Housing in Deptford
On the valuation list Deptford counts about 14,290 homes, 85% flats and 15% houses; 9% predate 1919, 4% are interwar and 84% post-war. Where most homes are flats, a flat in Deptford has no householder permitted development rights, so extending one needs planning permission and the freeholder's consent.
The drain run decides the route for a Deptford extension
Before a Deptford extension is drawn in detail, find the drains. Lewisham uses a full plans application for any new proposal to build above or within 3 metres of a drain or sewer, so the quicker building notice route is off the table for an extension that lands near a drain run. Lewisham's guidance also says you must apply for a build over agreement before doing any works if your home is within 3 metres of a public drain or 1 metre of a public lateral drain. Those are two permissions from two bodies, the second from the water company, so a camera survey comes first.
On site, Lewisham Building Control's typical inspection stages include excavation, foundations, damp-proof course, drains inspection and testing, insulation and completion of building. Terraced houses are 14% of Deptford's homes, and on a terrace the garden may be reached only through the house, so every stage is booked ahead with the inspector. The trench stays open until it has been seen, and the new drain run is tested before it is backfilled, because a missed visit means digging out again. Lewisham sends a full plans decision within five weeks, unless a three week extension has been given, so the survey and design need to start early.
Building extensions on Deptford plots
Deptford's house plots vary widely, from the longer gardens of the older terraces to tight urban footprints closer to the creek and the high street. We plan each extension around the space you actually have, the fall of the drains and the position of any shared boundary. Where the new foundations run alongside or beneath a neighbour's wall, the Party Wall Act applies, and you serve the required notices before the groundworks begin, as building owner or through your surveyor. We give you the drawings and programme they need.
Structural work such as foundations, beams and the opening between old and new is controlled under building regulations, with building control inspecting at key stages. This is separate from planning permission, which governs whether you may build at all. Your designer takes the planning side and we coordinate building control, then complete the roof, windows, insulation, wiring, plumbing and internal finishes so you receive a finished, signed-off room rather than a shell that still needs trades.
Kitchen extensions in Deptford
85% of homes in Deptford are flats, and a flat has no householder permitted development, so a ground-floor flat's kitchen extension needs planning permission from Lewisham Council and the freeholder's consent. Most kitchen extensions here are on the 15% of homes that are houses. The fit-out is priced on its own page, kitchen renovation in Deptford; the build figures are in the table above. Double storey extensions belong to the few houses here.
- Drainage diversion and build-over agreements with the water authority
- Steel goalpost frames where the rear wall opens up
- Foundations, groundworks and steel frames
VOA Council Tax stock of properties, March 2025, for Deptford North, Silwood & Pepys and New Cross & Deptford South. Counts rounded by the VOA.
Why Deptford Homeowners Choose GS Renovation
Homeowners across SE8 choose GS Renovation because we deliver the whole extension under one roof, from Lewisham planning advice to steelwork, roofing and decoration. We are used to working sensitively on period and listed townhouses, keeping the new addition faithful to the original house, and our founder's 30+ years on the tools mean fewer surprises and a genuinely finished result.
- One point of contact on the phone, not a call centre
- Drainage diverted or built over with the right approval in place
- 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…
Giorgio is an excellent and intelligent workman, and with very reasonable prices! He installed a kitchen extractor fan in a complicated situation…
FAQ
Frequently Asked Questions about House Extensions Deptford
Is the price of house extensions higher in Deptford than elsewhere in South East London?
Location is not a line on a house extensions quotation in Deptford; two South East London homes of the same age get similar figures within £2,000 to £2,800 per m² for a rear extension (indicative). What separates them is condition and access at the SE8 address, and the approvals route, since the work needs building regulations approval from foundations to completion. There is no travel surcharge within Lewisham.
Does my Deptford extension need planning permission or just building regulations?
A modest single storey rear extension on a standard Deptford house is often permitted development, needing only building regulations. But if you want a double storey or wrap-around, or a side extension in a conservation area, you will likely need planning permission from Lewisham Council, and a listed home needs listed building consent. We check your address first and advise before drawing anything.
Can a Deptford flat owner use permitted development to extend?
No. Only houses carry permitted development rights for a rear extension; flats and maisonettes have none, so extending a Deptford flat means a planning application to Lewisham Council plus the freeholder's consent under the lease. With 85% of Deptford dwellings being flats, it is worth confirming which you own before drawings start.
What if a public sewer runs under my Deptford extension footprint?
Building over or close to a public sewer needs the water company's consent under Part H, and that can shape the foundation design or the position of the extension. A drainage survey with a camera before design shows where the pipes run, so the plans go to building control with the sewer already accounted for.
Do party wall rules apply to an extension on a Deptford terrace?
Often. Digging trenches within 3 metres of next door and deeper than its footings triggers one month's notice under the Party Wall Act. Deptford terraces sit tight together, so that is the normal case. Should the neighbour dissent, surveyors settle an award, which takes weeks, so it pays for you (or your surveyor) to serve notice while the drawings are still with building control.
How is a Deptford house extension joined to the original rooms?
The new shell is built, roofed and made watertight while the old rear wall still stands, so the house is never open to the weather. Only then is the wall propped and broken out, with steel on padstones taking the load above. The extension must meet current Part L insulation standards, which sets the wall and roof build-up.
What does Lewisham's Local Plan say about the size of a Deptford extension?
The Lewisham Local Plan says extensions to residential buildings should normally be subordinate in scale to the original building. The test is the original building, so a rear addition built by an earlier owner does not enlarge the base that a new extension is measured against. On a small house near Deptford High Street that can mean a single storey rear extension sits comfortably while a full width, two storey one does not. Have the designer show the original footprint on the drawings.
Can a ground floor flat in Deptford be extended into its garden?
It can, but only with planning permission. Householder permitted development rights belong to houses, not flats, and Lewisham says flats or subdivided houses in conservation areas must seek planning permission for changes to the exterior. With 85% of Deptford homes being flats, this is the usual case here. A leaseholder also needs the freeholder's consent, and the garden may be part of the lease or kept by the freeholder. Check both before the designer draws anything.
Can a Deptford homeowner get written planning advice on an extension before applying?
Yes, through Lewisham's Duty Planner Standard Service, which gives written advice from a planning officer on simple homeowner projects. It covers simple householder extensions and alterations not within a conservation area, so it suits a straightforward rear extension on a Deptford house outside one. For a house inside a conservation area the service lists window replacement but not extensions, so ask Lewisham which advice route applies there. Take the written reply to the designer before drawings are finalised.
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