House Extensions Finchley
Single storey rear and double storey extensions in Finchley, 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 across Finchley, where the interwar semis and larger period houses sit on generous plots with room to grow. We handle the groundworks, the steel, the roof and the full fit-out as one accountable project.
In Finchley, 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 Finchley: 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 Finchley
Finchley range: choose above
Rear and side-return extensions in Finchley
The wide plots typical of Finchley suit generous single storey rear extensions and side infills that fill in the gap alongside the original 1930s footprint. We start with foundations and groundworks suited to the local ground, then bring in steel beams where the back wall is removed to join the extension to the existing house. A well-planned rear extension turns the cramped original kitchen into an open-plan kitchen-diner opening onto the garden.
Double storey and wrap-around extensions are also popular on the larger interwar homes near Hampstead Garden Suburb and towards Mill Hill, adding a bedroom and en-suite above a widened kitchen. We match brickwork and roof pitch to the existing house so the addition reads as part of the original build, and we handle the roof works, windows, insulation and full internal fit-out through to decoration.
Housing in Finchley
On the valuation list Finchley counts about 19,250 homes, 59% flats and 41% houses; 38% predate 1919, 26% are interwar and 36% post-war. A flat in Finchley 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.
Rear extensions under the Finchley Garden Village design guidance
Finchley Garden Village has its own design guidance, and it rewrites the usual rear extension. Single-storey rear extensions should generally not be wider than half the width of the rear elevation and should be of a modest depth. Their height should be kept to a minimum and respectful of the window sills above, and flat-roofed extensions will not be permitted. In practice that means a narrow, pitched or mono-pitched addition kept low beneath the first-floor sills, not the full-width flat-roofed box seen on other Finchley streets. The roof pitch then sets the internal ceiling height, so the kitchen layout and any rooflights are designed around it.
The Community Infrastructure Levy applies here as it does across the borough. Barnet Council adopted its revised charging schedule on 1 March 2022, and it came into effect on 1 April 2022, with a residential rate that covers C3 homes. A larger extension can be liable, and an owner extending their own home can claim an exemption, but the claim has to reach the council before work starts, with the commencement paperwork in order. We put that step into the programme, because a Finchley extension that starts on site first puts the exemption at risk.
Planning and party walls in N3
Some Finchley extensions fall under permitted development, while others need a full planning application to Barnet Council. It depends on the size, the height, how close you build to the boundary and whether your street or property carries any restrictions. Homes inside a conservation area, such as Hampstead Garden Suburb, face tighter controls, with side and two storey extensions needing an application. We assess your specific property early and tell you honestly which route applies before any design is finalised.
Whichever route you take, the structural work still needs building regulations approval and inspection, which is separate from planning. Because these are semi-detached and closely spaced houses, excavating foundations near the boundary or building onto the shared wall brings the Party Wall Act into play, so you serve notices on neighbours in good time as building owner. We coordinate planning and building control and give you the drawings the party wall notices need, so nothing stalls the programme.
Kitchen extensions in Finchley
59% of homes in Finchley are flats, and a flat has no householder permitted development, so a ground-floor flat's kitchen extension needs planning permission from Barnet Council and the freeholder's consent. Most kitchen extensions here are on the 41% of homes that are houses. The fit-out is priced on its own page, kitchen renovation in Finchley; the build figures are in the table above.
Double storey extensions in Finchley
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 Finchley often needs planning permission from Barnet Council. With 25% of homes here semi-detached or detached, the side of the house is often an option too. Finchley Church End Conservation Area was designated by Barnet Council in July 1979 (council source). Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.
- Building control inspections at foundation, damp course and steel stages
- Single and double storey extensions
- Steel goalpost frames where the rear wall opens up
VOA Council Tax stock of properties, March 2025, for all 5 statistical areas in Finchley. Counts rounded by the VOA.
Why Choose GS Renovation in Finchley
Finchley homeowners choose GS Renovation because we manage the whole extension, from foundations and steel to the roof and the final coat of paint, with one team answerable for the result. We advise clearly on permitted development versus a Barnet Council planning application, give you the drawings for the party wall notices you serve on your semi, and bring our founder's 30+ years of building to every stage.
- Weathertight shell reached before the fit-out begins
- Building control inspected at foundation, damp course and steel stages
- Honest updates if a date or a detail has to move
Built a new extension at rear of property. Laid foundations, drainage, raised floor, new roof and completed all fixtures and interior decoration…
The kitchen has been fitted to the high standard. Saaid was polite, professional, tidy, he pays attention to a little details that make huge…
Saiid did a complete refurbishment of our small bathroom. This involved ripping out the existing bath/shower, basin, toilet, pipework, and tiles and…
FAQ
Frequently Asked Questions about House Extensions Finchley
Why do house extensions quotes in Finchley vary so much?
House extensions quotes in Finchley spread widely because scope, not skill, is what differs. A figure that omits the engineer's design, the Barnet Council building control fee or the making good will always undercut one that includes them. Sequence is where cheap quotes cut corners: the steel into the house is designed before the rear wall comes down. GS Renovation lists each element for the N3 address against £2,000 to £2,800 per m² for a rear extension (indicative).
Can a Finchley extension be built over a manhole?
Sometimes, with agreement and the right arrangement. Where a manhole sits within the footprint of a proposed Finchley extension, the options are diverting the drain, relocating the chamber outside the building or building over it with a sealed double cover and maintained access. Any of these needs the water authority's agreement where the drain is shared. The position is established by survey before the design is fixed.
What insulation standard applies to a Finchley extension?
The standard current when the work is approved, which is considerably higher than the existing house. A Finchley extension has to meet requirements for walls, floor, roof and glazing, along with airtightness and the efficiency of any heating within it. That affects wall thickness and therefore internal space. Designing to those figures from the outset avoids a redesign when the application is assessed.
Is there a limit on glazing in a Finchley extension?
There is a balance to strike rather than a simple limit. Large glazed areas in a Finchley extension lose heat in winter and gain it in summer, and the energy calculation for the work has to balance overall. Where the design is heavily glazed, that is offset by better performance elsewhere in the construction. It is worth resolving early, because it can change the specification of the glazing itself.
Who owns the boundary wall beside a Finchley extension?
The title deeds decide it, and the answer affects what can be built. At your Finchley property the boundary may belong to one side, be shared, or be a party fence wall, and building off it or against it has different implications in each case. Where it is shared, the Party Wall etc. Act applies. Establishing ownership before the design assumes a foundation on that line prevents a dispute later.
What happens to the guttering where a Finchley extension joins the house?
It is rerouted, because the original run usually discharges straight onto the new roof. At your Finchley property the existing gutter and downpipe serving the rear elevation are relocated to suit the extended footprint, and the new roof drains to its own outlet. Leaving the old arrangement in place concentrates water at the junction, which is the first place a flat roof fails.
Will a two storey extension be approved in Finchley Garden Village?
It is unlikely. The village design guidance says two storey extensions can significantly alter the character and appearance of a property and are therefore unlikely to be supported. Plan the extra space on one storey, within the width and height limits the same guidance sets, rather than paying for a two storey design that starts from a weak position. The Article 4 Direction there, introduced in September 1979, also means smaller external changes may need an application.
What applies to an extension in the Hampstead Garden Suburb Conservation Area?
Two separate consents, one from Barnet Council and one from the Hampstead Garden Suburb Trust, and work waits for both. Width is the first design limit to check: the Suburb's guidance caps a rear extension at half the width of the back of the house as a general rule, and asks for less in most instances. Draw the narrower option first and submit identical drawings to both bodies.
Which Barnet plan is a Finchley extension application decided under?
The one in force when the decision is made. The Planning Data record for the Barnet Local Plan document, published by the London Borough of Barnet, gives a start date of 2025-03-04. A design statement for a Finchley extension should quote that plan, not older borough documents, and approvals on the street from before that date show what was acceptable then, not what is acceptable now.
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