House Extensions Chelsea

GS Renovation builds extensions on Chelsea's period homes, from Georgian townhouses near the King's Road to Victorian properties across SW3. We handle foundations, steelwork, roofing and fit-out, and guide you through whether your project is permitted development or needs full planning permission.

In 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 Chelsea: the structural engineer we appoint designs the structure, we build it, and building control signs it off.

Rear and side-return extensions in Chelsea

The most common extension across Chelsea's period stock is a rear or side-return addition that widens a cramped kitchen at the back of the house. We dig and pour new foundations, taking care around the mature trees and neighbouring structures typical of SW3 gardens, then build up in brick or with large glazed openings. Steel beams sized by a structural engineer carry the new openings and any removed rear wall, all inspected under the Building Regulations.

On larger plots we build double-storey and wrap-around extensions that add bedrooms and bathrooms above the new ground floor space. Whether your extension is permitted development or needs a full planning application depends on the property, and in Chelsea that balance tips towards planning because so much of the area is conservation-designated or listed. We assess your home, arrange the drawings and submit to the Royal Borough of Kensington and Chelsea where consent is required.

Housing in Chelsea

Chelsea counts roughly 12,410 homes for Council Tax; 57% are older than 1919, 11% interwar and 31% post-war, with 79% flats and 21% houses. Most homes here are flats, and a flat in Chelsea has no householder permitted development rights, so extending one needs planning permission and the freeholder's consent.

Rear building lines and extension limits in Chelsea

Before a Chelsea rear extension is drawn, look at the backs of the houses either side. Where the extension needs planning permission, Policy CL9 of the Consolidated Local Plan resists one that would extend rearward beyond the existing general rear building line of any neighbouring extensions. What the neighbours have already built therefore sets the depth you can realistically ask for. A measured survey that picks up the adjoining extensions, not only your own boundary, is worth commissioning first. Elsewhere in the borough, the council's appraisal for the Brompton Conservation Area lists oversized rear extensions and roof additions among the negative elements harming that area. Bulk is judged as well as depth.

Only 21% of Chelsea's homes are houses, and flats do not benefit from permitted development rights, so an extension to a flat is a planning application plus the freeholder's consent from the outset. A house may have permitted development rights for a modest single-storey rear extension, even in a conservation area, though a listed house still needs listed building consent. Kensington and Chelsea is in Mayoral CIL charging Band 1. Ask the designer at the start whether the new floor area makes the scheme liable and which forms must be submitted before work begins. That paperwork is far easier to settle at drawing stage than after the foundations are poured.

Planning and party walls in Chelsea

Chelsea sits almost entirely within conservation areas overseen by the Royal Borough of Kensington and Chelsea, and many townhouses are individually listed. In a conservation area a side, two-storey or roof extension always needs planning permission, while a single-storey rear extension within the limits can still be permitted development unless an Article 4 direction removes it, so the Royal Borough's Article 4 list is checked for your street. A listed house needs listed building consent for any extension. We advise honestly on what is achievable, arrange drawings that respect the Georgian and Regency character, and manage the application so your project starts on solid legal footing.

Because these houses are terraced, extensions almost always trigger the Party Wall etc. Act 1996, with excavation near the boundary and building against shared walls. You serve the correct notices and work with party wall surveyors before breaking ground. Once the shell is complete, our team handles the full fit-out, including plastering, electrics, plumbing, heating, flooring and decoration, so you deal with one contractor from foundations through to the finished, habitable room.

Kitchen extensions in Chelsea

79% of homes in 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 21% of homes that are houses. The fit-out is priced on its own page, kitchen renovation in Chelsea; the build figures are in the table above.

Double storey extensions in Chelsea

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 Chelsea often needs planning permission from the Royal Borough of Kensington and Chelsea. It is a job for the 21% of homes that are houses; a flat cannot add a storey this way. The Chelsea Conservation Area was designated in 1983, amalgamating the former St Luke's, Markham and Milner Conservation Areas (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
• Planning applications and permitted development assessments
• Flat and pitched roofs with rooflights or lanterns

VOA Council Tax stock of properties, March 2025, for Chelsea Manor & Royal Hospital, Chelsea Riverside East and Chelsea Riverside West. Counts rounded by the VOA.

For the wider picture around house extensions in Chelsea, see RSJ and steel beam installation in Chelsea, house extensions across Kensington and Chelsea, side return infills, party walls and extensions, our London house extensions page and Side Return vs Rear Extension.

Why Choose GS Renovation in Chelsea

Homeowners across SW3 choose GS Renovation because we manage the entire extension in-house, from arranging the planning drawings to groundworks, steel, roofing and finishing. With our founder's 30+ years on the tools, we understand the conservation and listed constraints on period townhouses and deliver work that respects their character.

• Drainage diverted or built over with the right approval in place
• Itemised pricing, so you can see what every stage costs
• Foundation depth set after trial holes, drains and trees are checked

Checked by Abdelaaziz Saaid, founder and director of GS Renovation Ltd (Companies House no. 14611254). Structural design is by the consulting engineer appointed to your project.