House Extensions Hampstead
Single storey rear and double storey extensions in Hampstead, 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 Hampstead, working with the bay-fronted Victorian and Edwardian terraces of NW3 and the larger villas nearer the Heath. We take on the foundations, the steelwork, the roof and the full fit-out, so your new space is built once and built properly.
In Hampstead, 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 Hampstead: 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 Hampstead
Hampstead range: choose above
Side-return and rear extensions in Hampstead
The classic Hampstead extension fills the side return alongside the rear closet wing, widening a narrow kitchen into a bright open-plan room facing the garden. We dig and pour the foundations, allowing for the mature trees and clay ground common across NW3, then form the new walls and roof. A steel beam sized by the engineer carries the original rear wall once it opens into the new floor area.
Wrap-around extensions take that side return and combine it with a rear projection to open up the ground floor of a terrace. Double-storey schemes add a bedroom or en-suite above. On homes near the village conservation area, external changes are handled sensitively, matching brick, pointing and window details so the addition sits comfortably against the period frontage rather than looking bolted on.
Housing in Hampstead
On the valuation list Hampstead counts about 11,670 homes, 78% flats and 22% houses; 63% predate 1919, 10% are interwar and 27% post-war. Most homes here are flats, and a flat in Hampstead has no householder permitted development rights, so extending one needs planning permission and the freeholder's consent.
Tree notice and the levy threshold for a Hampstead extension
Where a garden in the Hampstead Conservation Area has trees near the planned footprint, the programme starts with them. Camden requires six weeks' notice before tree work in a conservation area, for any tree with a trunk diameter of more than 75mm at a height of 1.5 metres. That captures much smaller trees than people expect. If a branch has to be cut back for scaffold, or a root is exposed in the trench, that notice period sits on the critical path, so the tree survey and the notice come before the foundation design is fixed.
Size matters in a second way. Camden's Community Infrastructure Levy applies to all proposals which add 100 square metres of new floorspace or an extra dwelling, and Camden's rate summary puts Hampstead in Zone C with Highgate. One modest rear extension sits well below that figure. A villa scheme that adds a side extension, a rear extension and a new lower floor can cross it once the areas are added together. We total the gross new floorspace at drawing stage, so whether the levy applies, and whether any relief has to be claimed before work starts, is settled before the application goes in.
Planning and party walls near Camden
Whether your extension is permitted development or needs a full planning application depends on the property. A modest single-storey rear extension may fall under permitted development, but side extensions in the Hampstead conservation area need permission from Camden Council, a listed building needs listed building consent, and larger or double-storey schemes almost always need permission. We advise honestly on which route yours takes before you commit to a design.
Because your extension builds off or against a shared boundary, the Party Wall Act typically applies, so you serve notice on the neighbour as building owner before we break ground, with the drawings and programme we give you. Alongside that, every extension is inspected under building regulations for foundations, structure, insulation and drainage. We coordinate the drawings, the party wall steps and the building control inspections so the whole project moves as one across NW3.
Kitchen extensions in Hampstead
78% of homes in Hampstead are flats, and a flat has no householder permitted development, so a ground-floor flat's kitchen extension needs planning permission from Camden Council and the freeholder's consent. Most kitchen extensions here are on the 22% of homes that are houses. The fit-out is priced on its own page, kitchen renovation in Hampstead; the build figures are in the table above.
Double storey extensions in Hampstead
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 Hampstead often needs planning permission from Camden Council. It is a job for the 22% of homes that are houses; a flat cannot add a storey this way. Camden publishes an Article 4 Direction schedule and list of properties affected in the Hampstead Conservation Area, excluding Frognal Way, under its heritage and conservation directions (council source). Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.
- Insulation, airtightness and thermal detailing to regulations
- Building control inspections at foundation, damp course and steel stages
- Foundations, groundworks and steel frames
VOA Council Tax stock of properties, March 2025, for Hampstead Town, Frognal and Fitzjohns & Royal Free. Counts rounded by the VOA.
Why Choose GS Renovation in Hampstead
Hampstead homeowners choose GS Renovation because we handle the extension end to end, from groundworks and steel to roofing, glazing and the final decoration. We are candid about whether you need planning permission or permitted development, we coordinate around the party wall award, and our founder's 30+ years on the tools means we build to suit these period terraces and villas.
- One point of contact from first survey to handover
- Foundation depth set after trial holes, drains and trees are checked
- 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 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 Hampstead
Is the price of house extensions higher in Hampstead than elsewhere in North London?
Location is not a line on a house extensions quotation in Hampstead; two North 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 NW3 address, and the approvals route, since the work needs a Camden Council building control inspection of the foundations before concrete is poured. There is no travel surcharge within Camden.
Does my Hampstead side-return extension need planning permission?
A single-storey side-return may be permitted development, but much of Hampstead sits within a conservation area and many homes are listed, which usually means a planning application to Camden Council. Double-storey and larger schemes generally need permission too. We assess your specific property, advise on the likely route and coordinate the architect's drawings and the application.
Can I build out into the garden from my Hampstead ground floor flat?
Possibly, but only through a planning application, since flats have no permitted development rights. In Hampstead, where 78% of homes are flats, most proposed extensions need Camden Council planning permission as a matter of course. The garden may also be held under a different title or shared with other leaseholders, and the freeholder's written consent is almost always required. We read the lease before sketching anything.
How do trees near a Hampstead extension affect the foundations?
Mature trees on clay ground draw moisture out of the soil, and clay shrinks and swells as it dries and wets. Foundations near trees in Hampstead are therefore often dug deeper than usual, and the engineer may specify a different foundation type altogether. Building control inspects the trenches before concrete is poured.
Can I add a side extension to a Hampstead house in a conservation area?
Not under permitted development. Conservation areas remove side extension rights for houses, and much of NW3 sits inside one, so a side extension needs planning permission from Camden Council. Rear extensions may still be possible under permitted development on a house, within the depth limits, but we check the property's status first. Building regulations apply either way.
Can we keep living in our Hampstead house while the extension goes up?
Usually yes, because the existing rear wall stays in place until the new shell is weathertight. Foundations, walls and roof go up outside, then the old wall is propped and opened with the steel as one of the last structural steps. Disruption inside the house peaks during that stage and when the new floor is joined to the existing one.
Which level of Camden pre-planning advice suits a two storey rear extension in Hampstead?
Level 2. Camden's Level 2 homeowner pre-planning application advice covers multiple or more complex works, such as more than one extension or two storey rear extensions. That is the level to book for a two storey scheme, or a rear and side extension together. In a conservation area both of those need planning permission, so bring a draft heritage statement to the meeting, since the application will need one anyway.
How does Camden's building control schedule band a Hampstead extension by floor area?
Camden's Schedule 2 residential charges have a line for any extension of a dwelling, including basements, whose total floor area exceeds 10m2 but does not exceed 60m2. Measure the planned area against that band early, since an extension plus a lower floor can move the job into a different line. Settle the areas with the architect before choosing between a building notice and full plans, so the charge in the budget matches the scheme that is actually submitted.
Does a self-contained garden annexe in Hampstead count as an extra dwelling for the levy?
If it is designed as a separate home, it can. Camden's Community Infrastructure Levy applies to proposals that add an extra dwelling, whatever the floor area, as well as to those adding 100 square metres. A garden room used with the house is a different thing from a studio with its own kitchen, bathroom and entrance. Settle which one you are building before the drawings are finished, because the answer changes the application and the cost.
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