House Extensions St John's Wood
Single storey rear and double storey extensions in St John's Wood, 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 St John's Wood, working on the detached and semi-detached villas near Regent's Park and Lord's as well as the smaller terraced houses and garden flats of NW8. We take a rear, side-return or wrap-around extension from foundations and steel through to the finished, fitted-out room.
In St John's Wood, 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 St John's Wood: 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 St John's Wood
St John's Wood range: choose above
Rear and side extensions in St John's Wood
The classic project on a St John's Wood villa is a rear kitchen extension across the garden elevation; on the smaller terraced houses it is a side infill beside the rear wing. Either widens a cramped kitchen into a proper family space. We dig and pour foundations to suit the ground and any nearby trees, then install a steel frame so the original rear wall can come out. A glazed roof or rooflights bring light deep into the plan where the house was previously dark.
Whether this needs planning permission depends on the property. Many single storey rear and side extensions fall under permitted development, but an Article 4 direction can remove it, so check Westminster's Article 4 list; in a conservation area it no longer covers side extensions or anything over one storey, while a listed home needs listed building consent. We check the exact position with Westminster City Council before design, so you know early whether a full planning application is required or not.
Housing in St John's Wood
The stock in St John's Wood runs to roughly 8,840 dwellings, 90% of them flats and 10% houses, built 23% before 1919, 31% between 1919 and 1939 and 46% after 1945. A flat in St John's Wood has no permitted development rights, so an extension needs planning, which matters here because most homes are flats.
Basements and garden extensions for St John's Wood villas
St John's Wood's villas are the part of the stock where an extension can go down as well as out. 5% of homes here are semi-detached or detached, and those are the houses most likely to have the garden depth that makes it possible. Westminster's city-wide Basement Development Article 4 Direction removes permitted development rights for basement development throughout the city, so any basement under a villa or its garden needs planning permission. City Plan Policy 50 then supports basements only where they do not extend beneath more than 50% of the garden land, with a separate allowance where the garden is 8m or less at its longest point.
The same policy supports no more than one storey beneath the lowest original floor level, with exceptions possible only on large sites, and applications should come with a structural methodology statement and self-certification from a suitably qualified engineer. For a St John's Wood villa, the garden is measured and the basement footprint set against the half-garden limit before any engineer designs the dig. Basement schemes consented from September 2016 onwards also carry Westminster's Code of Construction Practice as a pre-commencement condition, so its requirements are in place before the first muck-away lorry arrives.
Double storey extensions across NW8 homes
On the wider plots around St John's Wood, including the detached and semi-detached villas, there is often room for a double storey rear extension that adds a kitchen-diner below and a bedroom or en-suite above. These carry more load, so the foundations and steel beams are sized accordingly by a structural engineer and signed off under building regulations by building control, which governs the structure regardless of the planning route.
Extensions on a semi-detached or terraced house almost always involve the Party Wall etc. Act, because you build up to or along a shared boundary, so you serve the notices in good time as building owner; we give you the drawings they need and build to any award. From groundworks to roofing, plastering, electrics and the final kitchen or bathroom fit-out, one team runs the programme, keeps the rest of the house liveable and coordinates every trade so the new space is finished, not just built to shell.
Kitchen extensions in St John's Wood
90% of homes in St John's Wood are flats, and a flat has no householder permitted development, so a ground-floor flat's kitchen extension needs planning permission from Westminster City Council and the freeholder's consent. With so few houses here, the realistic kitchen gain in most St John's Wood homes is a better layout inside the flat rather than an extension. The fit-out is priced on its own page, kitchen renovation in St John's Wood; the build figures are in the table above. Side return extensions belong to the few houses here.
- Steel goalpost frames where the rear wall opens up
- Brickwork and mortar matched to the existing elevation
- Drawings and the structural engineer's design coordinated for you
VOA Council Tax stock of properties, March 2025, for St John's Wood North and St John's Wood South. Counts rounded by the VOA.
Trusted House Extensions in St John's Wood
Homeowners in St John's Wood choose GS Renovation because we manage the whole extension, the planning check with Westminster, the foundations, the steel and the fit-out, under one contract. With our founder's 30+ years on the tools, we give honest advice on what your plot and its conservation status will allow, and finish to a standard that suits the area.
- Founder with 30+ years of hands-on experience
- Foundation depth set after trial holes, drains and trees are checked
- Insulation and thermal detailing to current regulations
Built a new extension at rear of property. Laid foundations, drainage, raised floor, new roof and completed all fixtures and interior decoration…
George always kept to commitments and arrived on time. He offered helpful suggestions during his initial visit and promptly provided a reasonably…
It's the second time I have hired George and he has been absolutely professional and the work he did resembles perfectly what I had in mind. Being an…
FAQ
Frequently Asked Questions about House Extensions St John's Wood
Does the cost of house extensions rise in a mixed-age St John's Wood property?
In a mixed-age St John's Wood home the unknowns behind plaster are what move a house extensions figure within £2,000 to £2,800 per m² for a rear extension (indicative), which is why the NW8 survey matters more there. GS Renovation prices the visible work, names the risks, and agrees anything additional in writing. The approvals do not change with age: permitted development or a planning application to Westminster City Council applies either way.
Do I need planning permission to extend my St John's Wood house?
Some single storey rear extensions to houses in NW8 are permitted development, including in a conservation area, but a conservation area removes it for side extensions and anything over one storey, an Article 4 direction can remove more, and a listed building needs listed building consent. Conservation areas and listing are both common in St John's Wood, and flats have no permitted development rights at all. We check your address with Westminster City Council first. Either way, the structure itself needs building regulations approval and building control sign-off.
If I own a St John's Wood villa, what does a double storey extension involve?
More than a single storey, both structurally and in consents. The foundations and steel carry two floors, so the engineer sizes them for that load, and building control inspects at each stage. Planning permission is needed from Westminster City Council. The new walls, floor and roof must meet current Part L insulation standards. The first floor room also needs an escape route agreed if it creates a third storey.
Does my St John's Wood extension need party wall notice for the foundations?
It does if the trench runs within 3 metres of your neighbour's building and deeper than their foundation. That needs one month's notice under the Party Wall Act before excavation. On a terrace that is almost certain. On a detached villa it depends on the distance to the next house, which is measured, not assumed. A dissent leads to a surveyor's award setting out the method.
What if a drain runs under my St John's Wood extension?
Mapping the drainage comes ahead of any foundation design. Pipework that serves your property alone is yours to reroute or bridge over. Anything shared with neighbouring houses is likely to be a public sewer, and Part H means the water company must agree before you build over or close to it; they sometimes want a camera survey first. Opening the inspection chambers during our survey tells us which case applies.
Can I extend my ground floor flat into the garden in St John's Wood?
Possibly, but not under permitted development, which applies to houses only. A flat extension needs a planning application to Westminster City Council, and in most cases the freeholder's written consent, because the lease usually covers the structure and often the garden. Building Regulations approval is still needed for the structure. Flats upstairs may also have rights over the garden.
Does a large St John's Wood villa extension attract Westminster's CIL?
It can. Westminster charges CIL per square metre on new dwellings of any size and on any development where the internal area of a new building, extension or change of use exceeds 100 square metres. A villa scheme that combines a new lower level with a ground floor addition can pass that threshold once the areas are added together. An exemption for extending your own home has to be claimed before work starts, so we give you the internal areas from the drawings early.
How much of a St John's Wood garden can a basement go under?
No more than 50% of the garden land, under City Plan Policy 50, with a separate allowance on small sites where the garden is 8m or less at its longest point. The policy also supports only one storey beneath the lowest original floor level, except on large sites. On a villa plot the garden is surveyed first and the footprint drawn from that measurement, because the planning test is geometric before it is structural.
Does a rear extension to a St John's Wood villa have to stay smaller than the house?
Where planning permission is needed in a conservation area, in effect yes. Westminster's Development and Demolition in Conservation Areas guidance says extensions should respect the scale and proportions of the existing building and must be architecturally subordinate to the main building. It also says full width rear extensions are generally not acceptable, except in certain circumstances at basement level. The St John's Wood Conservation Area, designated in 1967 and extended in 1979 and 2007, brings that test to addresses within it. A single-storey rear extension within permitted development limits avoids it where those rights survive.
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