House Extensions New Cross
Single storey rear and double storey extensions in New Cross, 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 throughout New Cross, working on the Victorian and Edwardian terraces among SE14's flats. We take on rear, side-return and wrap-around projects, handling the groundworks, steelwork, roof and full fit-out so your enlarged home feels part of the original house.
In New Cross, 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 New Cross: 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 New Cross
New Cross range: choose above
Side-return and rear extensions in New Cross
The classic New Cross extension fills the side return, that narrow strip of open ground beside the original closet wing that so many SE14 terraces still have. Infilling it widens the kitchen dramatically and floods the plan with light through a glazed roof. We dig and pour foundations to suit the local ground, tie the new brickwork into the existing wall, and install the steel that lets us open the rear of the house right up.
A rear extension pushes the ground floor further into the garden, and a wrap-around combines both moves for a generous open-plan kitchen-diner. In terraces this close together the party wall almost always comes into play, so you serve notices on the neighbours early, with the drawings we supply. We build the shell, fit the roof and glazing, then complete the plastering, flooring, electrics and decoration as a single continuous project.
Housing in New Cross
Roughly 12,080 dwellings sit on the valuation list for New Cross. 28% are houses and 72% flats, and by age 43% predate 1919, 2% are interwar and 49% post-war. A flat in New Cross has no householder permitted development rights, so extending one needs planning permission and the freeholder's consent, which matters here because most homes are flats.
Extending a terrace house behind New Cross Road
Behind the commercial buildings of New Cross Road lies the terrace housing that makes up the rest of Lewisham's Hatcham conservation area, designated in 1990. When an extension to one of those houses needs a planning application, it has to be accompanied by a heritage statement, which Lewisham requires for every application affecting a building in a conservation area. The statement describes the house, the row and what the extension does to them. It is written from a measured survey and photographs of the rear elevations along the terrace, so commission it alongside the drawings, because what it finds can change the design.
The Lewisham Local Plan says extensions to residential buildings should normally be subordinate in scale to the original building. In a Victorian terrace the original building already includes its rear wing, so a new extension is judged against the house with that wing, not against a later lean-to or conservatory added by a previous owner. Terraced houses make up 25% of New Cross homes, and on a row of them the neighbours' extensions set a pattern too. Ask the designer to draw the original footprint and the extensions either side on the same plan.
Planning and permitted development in New Cross
Whether your New Cross extension needs planning permission depends on the property. Many single-storey rear and side-return projects fall under permitted development, which means no full application to Lewisham Council, though we still confirm the size limits and often recommend a lawful development certificate for certainty. In a conservation area such as Telegraph Hill, a side-return infill counts as a side extension and needs planning permission, though a single-storey rear extension can still be permitted development unless an Article 4 direction removes it. Double-storey work or anything unusually large is more likely to need a full planning application.
Separate from planning, every extension must satisfy building regulations. Building control inspects the foundations, the steel beams, the insulation, the drainage and the structure as the job progresses. We keep planning and building control clearly apart, because they answer different questions, and we keep both moving with Lewisham Council so nothing stalls halfway through your SE14 build.
Kitchen extensions in New Cross
72% of homes in New Cross 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 28% of homes that are houses. The fit-out is priced on its own page, kitchen renovation in New Cross; the build figures are in the table above.
Double storey extensions in New Cross
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 New Cross often needs planning permission from Lewisham Council. It is a job for the 28% of homes that are houses; a flat cannot add a storey this way. Lewisham's Hatcham conservation area, designated in 1990, is made up of commercial buildings on New Cross Road with terrace housing behind (council source). Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.
- Full fit-out, finishing and making good
- Building control inspections at foundation, damp course and steel stages
- Side-return and rear extensions
VOA Council Tax stock of properties, March 2025, for New Cross Gate, New Cross South and Telegraph Hill. Counts rounded by the VOA.
Why New Cross Homeowners Choose GS Renovation
GS Renovation gives New Cross homeowners one accountable team from foundations to final coat. We appoint the structural engineer, install the steel, give you the drawings for the party wall notices to neighbouring terraces, and handle the building control inspections, while advising honestly on whether your project is permitted development or needs planning. Our founder's 30+ years of experience keeps your SE14 extension on programme and built to last.
- Brick and mortar matched to the existing elevation
- A written scope and programme agreed before work starts
- Drainage diverted or built over with the right approval in place
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 New Cross
What does the house extensions quotation for a New Cross home cover?
A New Cross quotation for house extensions sets out scope, programme and price on one document, within £2,000 to £2,800 per m² for a rear extension (indicative). It shows what is done, in what order and at what cost, and the order is not arbitrary: the planning route is confirmed before drawings, and footings inspected before concrete. Exclusions are stated plainly rather than left to be discovered once work starts at the SE14 property.
Will my New Cross side-return extension need planning permission?
Often it will not. Many single-storey side-return and rear extensions in SE14 qualify as permitted development, so no full application to Lewisham Council is required, though in a conservation area such as Telegraph Hill a side-return infill needs planning permission, and a larger footprint or a double storey may too. Either way, the work still needs building regulations approval, and we confirm the correct route and handle building control before we start on site.
Can I extend a ground-floor flat in New Cross under permitted development?
No. Permitted development for extensions applies to houses, not flats or maisonettes, so an extension from a ground-floor flat needs planning permission from Lewisham Council. The freeholder's consent is usually needed as well, since the garden and outer walls may not be in your demise. Building regulations then apply to the construction, exactly as they would for a house.
Why does drainage decide so much when infilling a New Cross side return?
Because on a terrace house the side return is often where the drains run: an inspection chamber, the kitchen gully and a rainwater pipe all in the strip you want to build on. A camera survey shows whether the run is private or a public sewer. A private drain is usually rerouted with correct falls under Part H; a public sewer needs the water company's consent.
How deep do extension foundations go on New Cross clay?
Deep enough to reach ground that stays put, which the inspector confirms in the open trench. London clay swells and shrinks through the year, more so near trees, so depths vary street to street. Because next door's Victorian footings are shallow, a new trench alongside them usually goes lower, and the Party Wall Act then gives the neighbour a month's warning.
How is light kept in the middle room once a New Cross side return is filled in?
From above. Where a terrace house loses the side window of its middle room, rooflights or a glazed roof over the infill replace it, placed where daylight reaches deepest. Steel opens the old side wall so the rooms join. Part L applies to the extension, so the balance of glazing and insulation is checked early rather than after the roof is ordered.
Can a New Cross homeowner get written planning advice on an extension?
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 New Cross house outside any conservation area, and the written reply goes to the designer before drawings are fixed. Hatcham is one conservation area here, so check the address first. Inside one, the service lists window replacement but not extensions, so ask Lewisham which advice route applies.
Does a new porch on a New Cross house need planning permission?
Where an Article 4 direction covering the house includes porches, yes. Lewisham lists the addition of a porch, including infilling an open porch, among the changes its Article 4 directions can bring under planning control. Lewisham also says its Article 4 directions only apply to houses in use as a single dwelling house. Ask Lewisham whether a direction covers the address and what it includes before a front porch or an enclosed entrance is designed, because it is a small job that can still need a full application.
How long does Lewisham take to decide building regulations plans for a New Cross extension?
On a full plans application, Lewisham Building Control sends its decision within five weeks unless a three week extension has been given. Lewisham splits the fee into two payments, with plan checking paid upfront when the council receives the application. For a New Cross extension, submit once the structural engineer we appoint has finished the foundation and beam design, so the decision covers the real scheme and the groundworks can be booked with it in hand.
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