House Extensions Kensington
Single storey rear and double storey extensions in Kensington, 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 Kensington, working within the constraints of W8's period townhouses and the conservation areas that cover much of the Royal Borough. We handle foundations, steelwork, roofing and a full fit-out on rear, side-return and wrap-around projects across the neighbourhood.
In Kensington, 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 Kensington: 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 Kensington
Kensington range: choose above
Rear and side-return extensions in Kensington
The side-return extension is a favourite in Kensington's period terraces, filling the narrow strip beside the rear closet wing to widen a kitchen into a bright open-plan space. We dig and lay new foundations, install the steel beams that carry the existing rear wall, and tie the new roof into the old. On the tighter plots common in W8, careful sequencing keeps the works manageable in an occupied home.
Because so much of Kensington falls within a conservation area, and many houses are listed, extensions here frequently need a planning application to the council rather than relying on permitted development: conservation areas remove it for side and two-storey rear extensions, and a listed house needs listed building consent as well. Whether your project is permitted development or needs planning permission depends entirely on the property, its listing and any past alterations. We assess this early, then coordinate the drawings and manage building control through to completion.
Housing in Kensington
The stock in Kensington runs to roughly 9,000 dwellings, 85% of them flats and 15% houses, built 75% before 1919, 6% between 1919 and 1939 and 19% after 1945. Where most homes are flats, a flat in Kensington has no householder permitted development rights, so extending one needs planning permission and the freeholder's consent.
Kensington rear extensions between the closet wings
Behind a Kensington townhouse, the obvious space to extend into is the void between the closet wings. The Kensington Conservation Area Appraisal notes that this void has frequently been infilled at lower ground floor level with conservatory type extensions, so a new infill joins an established pattern rather than breaking one. Depth is the limit. Policy CL9 of the Consolidated Local Plan resists an extension that would extend rearward beyond the existing general rear building line of any neighbouring extensions. The neighbours' infills, not the length of your garden, set how far the new room can reach.
Building in that slot is tight work. On one side the wall may be your own closet wing and on the other the neighbour's, so new foundations sit close to two sets of old footings. The building owner serves notice on the neighbour where the Party Wall Act applies. The new roof has to shed water without discharging onto the neighbour's side, and its junction with the old rear wall is where leaks start, so the flashing detail is drawn rather than improvised on the day. Spoil and materials travel through the house, which sets the pace of the dig.
Planning and party walls in Kensington
Permitted development rights are restricted on many of Kensington's period homes. In a conservation area a single-storey rear extension can still be permitted development within its limits unless an Article 4 direction removes it, but side and two-storey rear extensions cannot, and a listed building needs listed building consent whatever the route. We are realistic from the outset about which route your extension needs, so you are not caught out later. Where planning permission is required, your architect or designer prepares the application to the Royal Borough of Kensington and Chelsea, and we coordinate it with the build and manage the conditions attached.
Extending a terraced Kensington house almost always involves the shared party walls on both sides, and often excavation near them for new foundations. That brings the Party Wall Act into play, so you serve notices on neighbours in good time. The structural elements, the steel beams and any wall removal, are separately signed off under building regulations by building control, keeping the whole build fully compliant.
Kitchen extensions in Kensington
85% of homes in Kensington are flats, and a flat has no householder permitted development, so a ground-floor flat's kitchen extension needs planning permission from the Royal Borough of Kensington and Chelsea and the freeholder's consent. Most kitchen extensions here are on the 15% of homes that are houses. The fit-out is priced on its own page, kitchen renovation in Kensington; the build figures are in the table above. Double storey extensions belong to the few houses here.
- Trial holes to set foundation depth near drains and trees
- Levels, drainage and landscaping made good around the new build
- Flat and pitched roofs with rooflights or lanterns
VOA Council Tax stock of properties, March 2025, for Kensington Abingdon and Kensington Gardens. Counts rounded by the VOA.
Trusted House Extensions in Kensington
Homeowners across Kensington choose GS Renovation because we understand the planning reality of a conservation-area borough and build to suit period proportions. From foundations to fit-out, one team manages the engineer, the council application and building control, so your W8 extension is delivered cleanly and lawfully, backed by our founder's 30+ years on the tools.
- Permitted development checked before you pay for a planning application
- Building control inspected at foundation, damp course and steel stages
- Paperwork and certificates handed over for when you sell
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 Kensington
Can I get a fixed price for house extensions at a W8 address?
A fixed price for house extensions at a W8 address is possible wherever the scope can be pinned down at survey. GS Renovation quotes most Kensington jobs as a fixed project price within £2,000 to £2,800 per m² for a rear extension (indicative), covering labour, materials and permitted development or a planning application to the Royal Borough of Kensington and Chelsea. Where an unknown sits behind plaster, it is named before starting, and any variation is agreed in writing.
Will my Kensington extension need planning permission or is it permitted development?
Much of Kensington sits within conservation areas and many houses are listed. A conservation area keeps permitted development for a modest single-storey rear extension unless an Article 4 direction removes it, but not for side or two-storey rear extensions, and a listed house needs listed building consent, so an application to the Royal Borough is commonly needed. We check your address, its designations and any earlier extensions at the start, then advise the correct route before design work begins.
Can I extend my Kensington flat?
Rarely. Flats are 85% of Kensington dwellings, and flats have no permitted development rights, so any extension needs full planning permission from the Royal Borough and the freeholder's written consent under the lease. Where a lower-ground or top-floor flat has space outside, the case can still be made, but the building's other owners have a say.
What party wall notices does a Kensington terraced house extension need?
Usually more than one. Building a new wall on the boundary, cutting into the existing party wall for a beam, and digging foundations within 3 metres of a neighbour's building below their footings each have their own notice. The party structure notice needs two months, the excavation notice one month. Where a neighbour dissents, a surveyor's award follows.
How does Part L shape a Kensington house extension in a conservation area?
It fixes the insulation standard the new walls, floor and roof have to reach, and big glazed areas have to be offset by better performance elsewhere. Where a conservation area expects traditional brick or render outside, the insulation usually goes on the inside face, which thickens walls and trims floor area. The Royal Borough's inspector sees it installed before boards close it in.
How do materials reach the back of a Kensington terraced house for an extension?
Normally straight through the house, because terraces seldom have rear access. Floors, stair and hall walls are boarded first, and skips or grab lorries are booked around parking and neighbours. Every bag of spoil from the foundations and every block for the walls travels the same route. That shapes the programme and the number of people needed, so it is planned before a start date is set.
Is a closet wing infill in the Kensington Conservation Area permitted development?
Usually not. Where the closet wing is original, an infill beside it extends beyond a side wall of the original house, and in a conservation area permitted development does not cover side extensions, two-storey rear extensions or cladding. The Kensington Conservation Area is one such area, so an infill there goes through a planning application. Flats have no permitted development rights at all, and a single-storey rear extension to a house stays permitted development only where no Article 4 direction removes it.
Who serves party wall notice for a Kensington closet wing infill?
The building owner, which means you rather than the builder. An infill sits tight against the neighbour's wing, and excavating for new foundations within three metres of their building and deeper than its footings brings in the Party Wall etc. Act. Excavation notice goes at least one month before work starts, and notice of work to the party wall itself at least two months before. We supply the drawings the notices and any award need, and build the dates into the programme.
Can the owner of a Kensington lower ground flat extend into the garden?
Only with planning permission and the freeholder's agreement. Flats do not benefit from permitted development rights, so even a small rear extension to a flat needs an application. With 85% of Kensington homes being flats, read the lease plan first: the garden may be demised to the flat, shared, or kept by the freeholder. Building on land outside your demise needs far more than a licence to alter, and the neighbours' extensions still set the depth under Policy CL9.
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