House Extensions Carshalton
Single storey rear and double storey extensions in Carshalton, 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 Carshalton, working with the interwar semis across SM5 and its older Victorian and Edwardian terraces. We handle foundations, steel, roofing and the full fit-out, and we tell you clearly whether your project is permitted development or needs an application to Sutton Council.
In Carshalton, 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 Carshalton: 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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Carshalton range: choose above
Kitchen, rear and side-return extensions in Carshalton
On Carshalton's interwar semis the usual project is a single-storey rear kitchen extension, turning a small back kitchen into a wide kitchen-diner that opens onto the garden; on the older terraces near the village it is a side-return infill beside the closet wing. Either way the kitchen is planned with the extension, so the drainage, the steel over the opening and the rooflights are set out around where the sink, hob and table will go. We dig and pour the foundations, tie the new structure into the existing solid brickwork and install the steel beams needed to open the back of the house. A glazed roof or rooflights then floods the deeper plan with light.
Wrap-around extensions combine the side return with a rear projection for even more space, popular where the interwar semis nearer Cheam offer a slightly more generous plot. Whether it is a modest rear addition or a full wrap-around, we sequence the groundworks, structure, roof and internal fit-out as one managed job, so your Carshalton home stays watertight and progresses steadily from footings to finish.
Housing in Carshalton
About 9,910 homes are listed for Carshalton, and the mix is 66% houses to 34% flats, with 38% built after 1945, 44% in 1919 to 1939 and 18% earlier. A rear extension on a semi in Carshalton digs beside the attached neighbour, so one party wall notice is usual, and 33% of homes here are semi-detached.
Extending a Carshalton house inside or beside a conservation area
Sutton describes the Carshalton Village Conservation Area as having a high standard of design and infill development with evidence of careful control. For a rear or side extension there, that sets the bar: materials, roof form, window proportions and how the addition sits against the original house all carry weight. Sutton warns that permitted development may not be available for properties in a conservation area. Side extensions and two storey rear extensions there need a planning application, while a single storey rear extension can still be permitted development unless an Article 4 direction removes it. Among Sutton's adopted Supplementary Planning Documents is the Design of Residential Extensions, and reading it before the drawings start saves a round of amendments.
Outside the village, the Carshalton Park Conservation Area was designated in 1993 and covers 14.2 hectares, with the historic Carshalton Park at its centre. A house near either area should be checked against the boundary maps before any design work. Sutton sells pre-application planning advice, and for a householder scheme the written reply generally comes within 10 working days. For a Carshalton extension in a conservation area, that reply is the cheapest way to learn what the officer thinks before the drawings are complete.
Planning and party walls in Carshalton SM5
Many single-storey rear extensions in Carshalton fall under permitted development, but this is not guaranteed. If your home has been extended before, sits on a corner plot, or falls within any local restriction, you will need a full planning application to Sutton Council. We assess your specific property first and advise honestly, rather than assuming, so there are no surprises once work is under way.
On a semi or detached house with room at the side or rear, a double-storey extension adds a bedroom or bathroom above a larger kitchen, and it almost always needs planning permission from Sutton Council, with the first-floor steel designed by the engineer from the start. Any extension involving excavation near a boundary or attaching to a shared wall brings the Party Wall Act into play, which is common on SM5's semis and terraces. You serve those notices as building owner; we manage the planning route and the building regulations and give you the drawings and programme the notices need, so the whole project stays on track.
Double storey extensions in Carshalton
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 Carshalton often needs planning permission from Sutton Council. With 53% of homes here semi-detached or detached, the side of the house is often an option too. The Carshalton Village Conservation Area was designated in 1968 and covers 44.6 hectares, primarily encompassing open parkland of historic significance (council source). Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.
- Foundations, groundworks and steel frames
- Planning applications and permitted development assessments
- Building control inspections at foundation, damp course and steel stages
VOA Council Tax stock of properties, March 2025, for Carshalton Village, Carshalton on the Hill and Carshalton Beeches & Banstead Road. Counts rounded by the VOA.
Why Choose GS Renovation in Carshalton
Carshalton homeowners choose GS Renovation because one team carries the extension from foundations to final coat. We advise honestly on whether Sutton Council planning is needed or your project is permitted development, bring in the engineer who sizes the steels, give you the drawings your party wall notices need and finish to a high standard. Our founder's 30+ years on the tools means fewer surprises and a genuinely accountable build.
- Foundation depth set after trial holes, drains and trees are checked
- One point of contact from first survey to handover
- Drainage diverted or built over with the right approval in place
Built a new extension at rear of property. Laid foundations, drainage, raised floor, new roof and completed all fixtures and interior decoration…
George was brilliant. Lovely bloke, very reasonably priced and a perfectionist to boot. He completed our small kitchen renovation with care and great…
Giorgio is an excellent and intelligent workman, and with very reasonable prices! He installed a kitchen extractor fan in a complicated situation…
FAQ
Frequently Asked Questions about House Extensions Carshalton
Do you charge for a survey before quoting house extensions in Carshalton?
GS Renovation charges nothing to survey an SM5 property for house extensions, because pricing house extensions in Carshalton unseen is guesswork. The visit confirms the scope, what approvals it needs (permitted development or a planning application to Sutton Council), and where in £2,000 to £2,800 per m² for a rear extension (indicative) the job sits. An itemised figure follows in writing. Call 07472 424 226 or email info@gsrenovationltd.co.uk.
Will my Carshalton rear extension need planning permission or is it permitted development?
Many single-storey rear extensions in Carshalton are permitted development, but if your home has already been extended, sits on a corner plot or breaches size limits, you will need a full application to Sutton Council. Double-storey extensions almost always need permission. We assess your SM5 property first and give you a clear answer before any commitment, then handle the route that applies.
What if a drain runs where my Carshalton extension will go?
Then the drain is settled before any trench is dug. A drain serving your house alone can be diverted, or bridged with lintels where the new wall crosses it. A public sewer, which often applies where two semis share a run at the back, needs the water company's consent to build over or close to. An early camera survey shows which you have.
Can I stay in my Carshalton house while the extension is built?
Usually, yes, because the extension goes up outside the existing rear wall until late in the job. Foundations, walls and roof are built with the house still sealed. The disruptive stage is the break-through, when the rear wall is propped, the opening formed and the steel installed; the kitchen is often out of use from then until the new floor and electrics are in.
Will trees near my Carshalton extension change the foundations?
They can. Roots draw moisture from the ground, so a foundation near a tree may need to go below the zone the roots dry out. Depth is set from the species, its distance and the soil found when the trench is opened, and building control inspects the excavation before concrete goes in. A trench within 3 metres of next door and below their footing also needs a party wall notice.
What insulation standard does a Carshalton extension have to meet?
Whatever Part L currently demands of new walls, floors and roofs, even when the semi it adjoins is from the 1930s. In practice that means fully filled cavities, insulation under the slab, and a roof built deep enough to hold its insulation layer. A big lantern or a run of rooflights eats into that heat-loss allowance. The new room ends up warmer than the interwar rooms beside it, so radiator sizes are worked out afresh.
Does the size of a Carshalton extension change the building control fee?
Yes, for a single storey extension. Sutton's fee schedule has one fee for a single storey extension under 40m2 and a higher one over 40m2, and each has its own regularisation fee. If the design sits just over the line, trimming the floor area slightly can bring it under. Settle the floor area on the drawings before submitting, so the fee matches the extension that is actually built.
What holds up the completion certificate on a Carshalton extension?
Usually the paperwork from other trades, not the building. Sutton's inspection schedule for an extension to a house says the completion certificate follows in 5 working days if the final inspection is OK and installer certificates are received. Missing certificates are the common hold-up: the electrician's, the gas or heating engineer's registration record, and the window and door installer's. Ask each trade for theirs on the day they finish, and pass them straight to building control.
What if a public sewer runs under the garden where a Carshalton extension will go?
Then the building regulations route is fixed. In Sutton, building work that will be near or cross public sewers needs a full plans application rather than a building notice. The water company may also need to agree the build over or a diversion. Find the sewer on the records and lift the inspection chamber covers before the footprint is fixed, because moving an extension a short distance can be simpler than building over the pipe.
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