House Extensions Willesden
Single storey rear and double storey extensions in Willesden, 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 house extensions across Willesden and Willesden Green, from single storey kitchen extensions and rear additions to full wrap-arounds on the Victorian and Edwardian terraces of NW10. We handle groundworks, steelwork, roofing and the complete fit-out, and we tell you honestly whether your plans are permitted development or need a planning application.
In Willesden, 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 Willesden: 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 Willesden
Willesden range: choose above
Kitchen extensions, side returns and rear extensions in Willesden
The bay-fronted terraces around Willesden Green and towards Harlesden nearly all have a side return, that narrow strip of open ground beside the rear closet wing. Filling it in is one of the most effective ways to widen a cramped Victorian kitchen and pull daylight in through a glazed roof. We dig and lay the foundations, tie the new structure into the existing brickwork, and open the flank wall with a steel beam.
A rear extension pushes further into the garden and often combines with the side return to form a wide, open-plan kitchen-diner across the back of the house. That is what a kitchen extension usually means on an NW10 terrace: the old closet wing kitchen, the side return and the back reception become one room, with a steel beam where the original rear and flank walls stood. On a terrace the neighbour's boundary wall shades the new width, so rooflights over the infill matter as much as the glazing at the back. We manage the groundworks, the drainage connections, the steelwork over the new openings and the roof, then complete the plastering, glazing and finishes so you deal with one team from the first trench to the last coat of paint.
Housing in Willesden
The Council Tax list puts Willesden at about 9,160 homes, 77% flats against 23% houses; 64% went up before 1919, 8% between the wars and 28% after 1945. Most homes here are flats, and a flat in Willesden has no householder permitted development rights, so extending one needs planning permission and the freeholder's consent.
Brent's depth limits for a Willesden rear extension
Brent's Residential Extensions and Alterations SPD sets the depths a planning application for an attached home is judged against. They are up to 6 metres from the original rear wall for a single storey addition at the back, and no more than 3 metres for one of two storeys. Inside the Willesden Green Conservation Area the question comes earlier. Brent's appraisal for it says a single storey addition at the back needs planning permission once it goes 3m past the original rear wall, or 4m for a detached house. Every one of those measurements starts at the original rear wall, so date any earlier rear addition before the drawings begin.
Then find the drains. Where an extension would sit over a public sewer, or come within three metres of one, Brent insists on full plans. Behind a Willesden terrace, a run serving more than one house can be a public sewer rather than a private drain. If it is, the quicker building notice route is not available, and the sewer owner's agreement joins the programme. A camera survey of the run before the architect draws the footprint costs far less than redesigning foundations once the trench is open.
Planning and party walls for Willesden extensions
Many single storey rear extensions on NW10 terraces fall under permitted development, meaning you can build within set size and height limits without a full planning application. Larger schemes, double storey additions, side extensions, anything to the front and any work to a listed building will need permission from Brent Council. In a conservation area a single storey rear extension within the limits can still be permitted development, but side and two storey extensions cannot, and Brent has Article 4 directions in some conservation areas, so check its Article 4 list for your street. We assess your specific house and tell you which route applies before you commit, rather than assuming.
Because Willesden terraces are attached, excavating foundations near the boundary and building up against the party wall triggers the Party Wall Act, so you serve notice on your neighbours as building owner before we start, and we give you the drawings it needs. Whichever planning route your project takes, the structure is separately covered by building regulations, and building control inspects the foundations, the steel and the drainage as the extension goes up.
Double storey extensions in Willesden
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 Willesden often needs planning permission from Brent Council. It is a job for the 23% of homes that are houses; a flat cannot add a storey this way. Brent's Willesden Green appraisal says a single storey rear extension beyond the original rear wall by more than 4m for a detached house, or 3m otherwise, needs planning permission in a conservation area (council source). Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.
- Side-return and rear extensions
- Building control inspections at foundation, damp course and steel stages
- Trial holes to set foundation depth near drains and trees
VOA Council Tax stock of properties, March 2025, for Willesden Green and Church End. Counts rounded by the VOA.
Why Willesden Homeowners Choose GS Renovation
Willesden owners choose GS Renovation because we build extensions end to end and stay honest about the rules. We know which NW10 projects are permitted development and which need Brent Council permission, we give you the drawings for the party wall notices you serve on these attached terraces, and our founder's 30+ years of building means the foundations and steel are done properly.
- Photographs kept at each stage for your records
- Brick and mortar matched to the existing elevation
- Programme planned around party wall notice periods before excavation near a neighbour
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…
The kitchen has been fitted to the high standard. Saaid was polite, professional, tidy, he pays attention to a little details that make huge…
FAQ
Frequently Asked Questions about House Extensions Willesden
How do you price house extensions in Willesden?
GS Renovation prices house extensions in Willesden project by project, never by the day, against £2,000 to £2,800 per m² for a rear extension (indicative). After the NW10 survey the figure is built up from labour, materials, the engineer's design, and the Brent Council building control fee, each priced in the order the work runs: drainage under the footprint is diverted before foundations are poured.
Does a Willesden extension need its own heating?
It needs to be included in the system rather than left to borrow warmth from the house. A Willesden extension is usually more glazed than the rooms behind it, so the heat requirement is calculated for the new space and emitters sized accordingly. Where the existing boiler is near its limit, that is established before the work rather than discovered in the first cold spell.
Can a Willesden extension be built off the boundary wall?
Only once ownership and condition are established. The boundary at your Willesden property may belong to one side, be shared as a party fence wall, or be in poor repair, and building off it without checking is how disputes start. Where the Party Wall etc. Act applies, notice is served by the owner. The wall's condition is inspected before any load is placed on it.
How does the roof of a Willesden extension meet the existing house?
At a flashed abutment with falls designed to carry water away from the joint. Where a Willesden extension meets the original rear wall, the roof covering is dressed into the brickwork and the falls are set so nothing ponds against the junction. That detail is where flat roofs on extensions leak first. It is specified in the design rather than resolved on site by the roofer.
Can a Willesden house be lived in during an extension?
For most of the build, and not comfortably at the end. A Willesden extension is largely built outside the existing walls, so the house stays usable until the rear wall is opened and the two are joined. That stage is disruptive and the kitchen is usually out of use for a period. Planning where to cook and wash for those weeks is worth doing in advance.
What happens to the existing rear roof in a Willesden extension?
It is usually rebuilt or extended rather than left untouched. Where a Willesden extension covers or abuts the rear addition, the existing roof over that addition is frequently the oldest element of the house and its falls and covering are inadequate. Dealing with it as part of the same work avoids returning to the same area, and the junction between old and new is designed properly.
What happens if a Willesden extension was built without building control sign-off?
It can be regularised after the event. Under Brent's building regulation charges guide a domestic single storey extension under 40m2 can go through full plans or a building notice beforehand, or through regularisation afterwards, and the regularisation charge is the higher one. Regularisation means opening up enough for the inspector to see the foundations, insulation and drainage. When buying a Willesden house with an unsigned extension, raise it before exchange.
Is CIL relief automatic on a Willesden home extension?
No. Brent has charged CIL under its Charging Schedule since 1 July 2013, and a home extension can qualify for relief where the applicant lives there as their main residence. Brent does not grant that relief on its own; the claim has to be made before commencement. Starting work first puts the relief at risk, so the claim goes in once any planning permission is granted and before the first trench is dug, with a copy kept on the project file.
Is Brent pre-application advice worth getting for a Willesden extension?
For a scheme near the SPD limits or in a conservation area, it usually is. Brent's PREAPP 1 service gives a householder a written view on extensions and alterations to a dwelling, with a target of 20 working days from receipt of the enquiry and fee. Allow those four weeks before the planning application, and send drawings that show the original rear wall and the neighbours' windows so the response deals with the real scheme.
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