House Extensions Belgravia
Single storey rear and double storey extensions in Belgravia, 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 on Belgravia properties, from the grand stucco townhouses to the compact mews houses tucked behind SW1's main terraces. Given how much of the area is listed or within a Westminster conservation area, every extension starts with the planning position. We manage groundworks, steel and fit-out as one project.
In Belgravia, 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 Belgravia: 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.
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Planning and permitted development in Belgravia
Extensions in Belgravia are rarely straightforward permitted development. Flats, most of the homes here, have no permitted development rights to extend. For houses, the Westminster conservation areas remove permitted development for side extensions, two-storey rear extensions and roof extensions, and a listed house needs listed building consent for any extension, so a full planning application to Westminster City Council is often needed. A single-storey rear extension within the limits can still be permitted development unless an Article 4 direction removes it, so check the council's Article 4 list for your street. We assess your property's exact status early, so you know whether you are looking at permitted development, planning permission, or listed building consent before any design is finalised.
Where a rear or side-return extension is feasible, we coordinate the architect's design and the engineer's foundation and structural scheme so they satisfy both the council and building control. On listed properties we work sympathetically with the original fabric, and we coordinate the drawings, applications and the information your party wall notices need so the approval process is handled properly from the outset.
Housing in Belgravia
The Knightsbridge, Belgravia & Hyde Park statistical area has about 6,020 homes on the Council Tax list: 67% pre-1919, 9% interwar and 23% post-war, with flats making up 71% and houses 29%. A flat in Belgravia 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.
What Westminster's conservation guidance means for a Belgravia rear extension
Westminster's Development and Demolition in Conservation Areas guidance says extensions should respect the scale and proportions of the existing building and must be architecturally subordinate to the main building. Where a Belgravia extension needs planning permission, that shapes the brief. A single-storey rear extension to an unlisted house may still be permitted development, unless those rights have been removed for it, but a side or two-storey extension needs an application, as does any extension to a flat. Ways to keep an addition subordinate include keeping part of the original rear wall in view and staying below the main cornice. A design that tries to become the new back of the house starts from the wrong place, because it runs against the guidance from the first drawing.
Two further documents sit alongside that guidance. The Belgravia Neighbourhood Plan was adopted on 7 March 2024, and the current City Plan was adopted by full council in January 2026 following a Partial Review. Both form part of the Development Plan an application in Belgravia is decided against. Reading the neighbourhood plan policies for your street at the outset stops an architect detailing a scheme that conflicts with a plan policy. We price and programme the build only once the design has been tested against those documents.
Rear and mews extensions in SW1
Belgravia's mews houses offer real potential for careful extension and remodelling, whether adding to the rear, reworking the roof or opening up the ground floor. These smaller SW1 properties often need steel beams to create the open living space owners want, all sized by a structural engineer and signed off by building control. We handle the groundworks, foundations and full fit-out under one team.
On the larger townhouses, rear extensions must respect the shared party walls, so you serve Party Wall Act notices as building owner before excavating or building against a neighbour's structure, with the drawings we supply. From foundations and steelwork to roofing, plastering, electrics and the final decoration, we deliver a finished extension that suits the period character and the standards expected on a Belgravia address.
Kitchen extensions in Belgravia
71% of homes in Belgravia are flats, and a flat has no householder permitted development, so a ground-floor flat's kitchen extension needs planning permission from Westminster City Council and the freeholder's consent. Most kitchen extensions here are on the 29% of homes that are houses. The fit-out is priced on its own page, kitchen renovation in Belgravia; the build figures are in the table above.
Double storey extensions in Belgravia
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 Belgravia often needs planning permission from Westminster City Council. It is a job for the 29% of homes that are houses; a flat cannot add a storey this way. Belgravia was first designated as a conservation area in 1968 and extended in 1977 and 1981 (council source). Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.
- Flat and pitched roofs with rooflights or lanterns
- First fix and second fix plumbing and electrics throughout
- Full fit-out, finishing and making good
VOA Council Tax stock of properties, March 2025, for the Knightsbridge, Belgravia & Hyde Park statistical area, which also covers parts of Knightsbridge. Counts rounded by the VOA.
Trusted House Extensions in Belgravia
GS Renovation understands that a Belgravia extension is shaped as much by listing and conservation rules as by construction. We establish the planning position with Westminster City Council first, then deliver foundations, steel, roofing and fit-out as one accountable team. With our founder's 30+ years on the tools, you get a compliant, well-built extension and no surprises.
- Programme planned around party wall notice periods before excavation near a neighbour
- Free follow-up visit after completion if anything needs attention
- Garden levels and access made good where the build meets outside
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…
Saaid is the best craftsman I have worked with. He knows what he is doing from the very beginning. He has a great knowledge of construction…
FAQ
Frequently Asked Questions about House Extensions Belgravia
Are there hidden costs with house extensions in Belgravia?
Every extra cost on house extensions in Belgravia needs your written agreement, and the foreseeable ones are already priced within £2,000 to £2,800 per m² for a rear extension (indicative). Work in stucco-fronted period housing around SW1 occasionally reveals something behind plaster; when it does, GS Renovation stops, costs it and waits for your decision. The sequence of work stays fixed: the steel into the house is designed before the rear wall comes down.
Can I extend my Belgravia property under permitted development?
Flats have no permitted development rights to extend, and in Belgravia's Westminster conservation areas side, two-storey and roof extensions need planning permission; a listed house also needs listed building consent for any extension. A single-storey rear extension on an unlisted house can still be permitted development within the limits, unless an Article 4 direction removes it. We check your property's status with the council first, then build to whatever consent applies, alongside building control sign-off for the structure.
Does my Belgravia extension affect the neighbours' foundations?
It might, and the Act spells out when. Excavation inside a 3 metre band from an adjoining house, taken lower than that house's footings, requires a month's written warning to its owner. In a terrace or a mews that band usually catches both sides. Should either owner refuse, surveyors produce an award before the digger arrives, so notices leave early in the design stage.
Can a Belgravia extension be built over the drain?
Possibly, but it needs finding out before design. A drain that serves more than one house counts as a public sewer, and building over or near it requires the water company's consent under Part H. A private drain can often be diverted or enclosed with an access chamber inside the new floor. In a mews, where drains run tight to the buildings, a camera survey comes first.
Is there a limit on glass in a Belgravia extension?
Part L sets one indirectly. An extension must meet current insulation standards, so a very glazed design has to make up the heat loss elsewhere, through better glazing units, thicker roof or wall insulation, or a calculation for the extension as a whole. On a listed house or within a conservation area, the look of the glazing is also weighed in the planning and consent decisions.
What paperwork will I need from my Belgravia extension?
The completion certificate from building control, the planning permission and, if the house is listed, the listed building consent, together with any party wall awards. Westminster City Council issues the completion certificate after the final inspection. A buyer's solicitor will ask for every one of these, so we hand them over as a single pack when the builders leave.
Is a full width rear extension possible on a Belgravia terraced house?
Where planning permission is needed, Westminster's conservation area guidance says full width rear extensions are generally not acceptable, except in certain circumstances at basement level. A basement is its own consent path: a city-wide Article 4 Direction in force since 31 July 2016 removes permitted development rights for basement development throughout Westminster. At ground floor, a narrower footprint that keeps part of the original rear wall visible is the design that starts from the guidance rather than against it.
Does a Belgravia extension attract the Community Infrastructure Levy?
Only above a size threshold. Westminster charges CIL per square metre on new dwellings of any size and on any development where the internal area of a new building, extension or change of use exceeds 100 square metres. For a Belgravia house the gross internal area of the proposed extension is measured at design stage, so you know which side of that line the scheme sits on before the application goes in.
Can Westminster give a view on a Belgravia extension before a planning application?
Yes. Westminster offers householder pre-application advice on alterations and extensions to an unlisted house or flat, given in writing with a 28 day timescale. Proposals that include basement development use a separate service with 1 meeting and written advice, on a 35 day timescale. For a Belgravia rear extension, a written response on the size and position is worth having before an architect details the elevations.
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