House Extensions Kensington and Chelsea
Single storey rear and double storey extensions in Kensington and Chelsea, 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 house extensions throughout Kensington and Chelsea, adding space to the period townhouses and mews properties of Notting Hill, Holland Park and South Kensington. We handle groundworks, steelwork, roofing and fit-out, working within the tight urban plots and conservation constraints typical of the Royal Borough.
In Kensington and Chelsea, 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 and Chelsea: 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 and Chelsea
Kensington and Chelsea range: choose above
Rear and side-return extensions in Kensington and Chelsea
Many townhouses across SW3 and W11 have a rear closet wing and a narrow side return that can be infilled to widen the kitchen and reception. On these period plots we dig foundations to suit the ground and neighbouring structures, install steel beams to carry the existing wall over the new opening, and tie the new roof and rooflights into the original fabric. The result is a lighter, more open ground floor without losing the character of the house.
Extensions may be permitted development or may need a full planning application to the Royal Borough of Kensington and Chelsea, and it depends entirely on the property. Much of the borough sits within conservation areas, and many townhouses are listed. In a conservation area side and two-storey rear extensions lose permitted development, while a single-storey rear extension keeps it within its limits unless an Article 4 direction removes it, and a listed house needs listed building consent whatever the route. We check the property's designation first, then advise on whether planning permission and listed building consent are required before any design is finalised.
Housing in Kensington and Chelsea
Kensington and Chelsea's housing, as the Council Tax list records it, is about 89,280 homes: 16% houses, 84% flats, with 65% pre-1919, 8% interwar and 26% built since 1945. Most homes here are flats, and a flat in Kensington and Chelsea has no householder permitted development rights, so extending one needs planning permission and the freeholder's consent.
Setting the depth of a Kensington and Chelsea rear extension
In Kensington and Chelsea the depth of a rear extension that needs permission is set by the neighbours before it is set by the designer. 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. So the first survey task sits outside your own boundary: measuring how far the extensions on either side and along the row already project, from the garden and from upstairs windows, and recording them on the drawings. A design that stops on that line starts the application on the policy's side, and one that goes past it starts an argument.
Size and design quality are read together. The Brompton Conservation Area Appraisal lists domestic extensions, including oversized rear extensions and roof additions, among the negative elements harming the area. The lesson for a rear elevation is an extension that stays subordinate to the house and keeps the pattern of the terrace readable. Permitted development offers little way round this: flats have none, and in a conservation area a house can only add a modest single-storey rear extension without an application, unless an Article 4 direction removes that too. We price from drawings that already respect the building line, because redesigning after a refusal costs months.
Groundwork and steel for Kensington and Chelsea plots
Building at the rear of a Notting Hill or Knightsbridge terrace means working in confined spaces between existing walls, so groundworks and material handling need planning. We assess foundations against neighbouring structures and drainage, form the new footings, and set the structural steel that carries the loads where the original rear wall is removed. The steel is sized by an engineer and inspected by building control at each stage.
Because the new work almost always meets a shared boundary, the Party Wall Act applies and you serve notices on adjoining owners, using the drawings we supply, before excavation near their foundations begins. We coordinate this alongside building control and, where relevant, planning conditions from the council. From groundworks through to the full internal fit-out, one team manages the extension so the finish matches the period proportions of the existing home.
Kitchen extensions in Kensington and Chelsea
84% of homes in Kensington and Chelsea 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 16% of homes that are houses. The fit-out is priced on its own page, kitchen renovation in Kensington and Chelsea; the build figures are in the table above. Double storey extensions belong to the few houses here.
- Wrap-around extensions and infills
- Side-return and rear extensions
- Full fit-out, finishing and making good
VOA Council Tax stock of properties, March 2025, for all 21 statistical areas in Kensington and Chelsea. Counts rounded by the VOA.
The GS Renovation Difference in Kensington and Chelsea
Kensington and Chelsea homeowners choose GS Renovation because an extension here is rarely simple: conservation areas, listed status, tight plots and party walls all come into play. We manage the planning versus permitted development question, the engineering and the build as one accountable project, with our founder's 30+ years of experience.
- Building control inspected at foundation, damp course and steel stages
- Foundation depth set after trial holes, drains and trees are checked
- Fully insured, with cover in place on every site
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 and Chelsea
What is the going rate for house extensions around Kensington and Chelsea?
Three Kensington and Chelsea builders will give three different numbers for house extensions in Kensington and Chelsea, usually because they have scoped three different jobs within £2,000 to £2,800 per m² for a rear extension (indicative). GS Renovation prices the W8 property after a survey and sets out labour, materials, approvals and making good in the order they happen: the planning route is confirmed before drawings, and footings inspected before concrete.
Will my Notting Hill extension need planning permission or is it permitted development?
Much of Notting Hill in W11 lies within conservation areas, and many houses are listed. A single-storey rear extension can still be permitted development in a conservation area unless an Article 4 direction removes it, but side and two-storey extensions cannot, so a rear extension there often needs a full planning application to the Royal Borough of Kensington and Chelsea, and listed properties also need listed building consent. We check your property's status first, then advise on the correct route before designing anything.
Does a rear extension on my Kensington and Chelsea townhouse involve both neighbours?
Usually both of them. In a terraced row, trenches that come within 3 metres of either adjoining house and go deeper than its footings bring in the Party Wall etc. Act 1996, and the notice period is one month. A townhouse with neighbours on each side will normally serve two notices. Where either owner withholds agreement, surveyors settle an award first, so we have the drawings for your notices ready well ahead of the dig.
Can an extension be built over the drains behind my Kensington and Chelsea house?
Possibly, but find out early. Where the drain behind a row of houses serves more than one property, it counts as a public sewer, and Part H means building on or close to it needs the water company's agreement. A private drain can usually be rerouted or given an access chamber within the new floor. A camera survey before the design is fixed shows exactly what runs under the footprint.
How can I get light into a Kensington and Chelsea extension between tall buildings?
From above, mostly. Between tall neighbouring walls, side windows add little, so rooflights, a glazed roof or a lantern bring daylight down into the deepest part of the plan. Part L caps how much glazing the extension can carry before better insulation elsewhere must compensate. A long rooflight along the junction with the old back wall often lights the original room as well.
Can we live in our Kensington and Chelsea townhouse during the extension?
Often, yes. On a multi-storey townhouse the upper floors stay habitable while the extension goes on behind the lowest level. The heavy disruption comes when the old rear wall is opened to join old and new with steel, after the new structure is weathertight. The kitchen may be out of action for a spell, so many owners set up a temporary one on a floor above.
Can a basement under the garden be part of a Kensington and Chelsea extension?
Only within limits set by Policy CL7. Basement development must not exceed a maximum of 50 per cent of each garden or open part of the site, and a minimum of one metre of soil is required above any part of a basement beneath a garden. The council's borough-wide Article 4 direction was made to remove permitted development rights for basement development, so plan on a planning application. The structural slab under the garden must then carry that depth of wet soil and planting.
Is a rear extension backing onto a Ladbroke communal garden judged more closely?
It is judged against an appraisal that names rear extensions directly. The Ladbroke Conservation Area was designated in 1969, one of the Royal Borough's earliest designations, and its appraisal lists poorly designed rear extensions among the negative features affecting communal gardens. For a house backing onto one of those gardens, the application drawings should show the extension as seen from the garden, with materials, roof edge and glazing detailed, not only a plan and a section.
When can the old rear wall be broken out for a Kensington and Chelsea extension?
On weekdays, inside the high impact windows. The Final Draft Code of Construction Practice lists all demolition and concrete-breaking among high impact activities, allowed from 9am to noon and from 2pm to 5:30pm, Monday to Friday. Taking down the old rear wall and lifting any concrete yard falls squarely within that. We time the break-through for after the new structure is weathertight, so the house is open to the extension for as short a spell as possible.
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