House Extensions Merton

GS Renovation builds extensions throughout Merton, working with the Victorian and Edwardian terraces of Wimbledon, the interwar terraces and semis of Mitcham and Morden, and larger suburban homes near Wimbledon Common and Morden Hall Park. Across SW19, SW20, CR4 and SM4 we draw on our founder's 30+ years on the tools to turn tight rear yards and unused side returns into bright, well-built living space.

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

Side-return and rear extensions in Merton

On the Victorian terraces around Wimbledon, the side return alongside the rear closet wing is the classic opportunity. Infilling that narrow strip and pushing the back wall out creates the kitchen extension and open-plan kitchen-diner that suits family life in SW19; on the interwar terraces of Mitcham and Morden, which have no closet wing, the same room comes from a rear extension across the full width. We handle the groundworks and foundations, the steel beams that carry the original rear wall, the roof with its rooflights, and the full fit-out inside.

Wrap-around extensions combine the side return with a rear addition for a larger footprint, while double-storey options add a bedroom above. On the semis and detached houses of the leafier SW20 streets there is often room to extend more ambitiously, always built to sit correctly against the existing structure.

Housing in Merton

The valuation list shows roughly 87,830 homes in Merton, of which 26% are pre-1919, 37% interwar and 36% post-1945, split 42% flats to 58% houses. Terraced houses make up 43% of homes here, and a rear extension on a terrace in Merton digs foundations close to both neighbours, so notices to both are normal.

Sewers, building notices and CIL on Merton extensions

In Merton a full plans submission must be made before work starts if the proposed extension is within 3 meters of a Thames Water sewer, and the building notice route is only available where the works are not within that distance. Behind a terrace, the drain running under the gardens can be a shared sewer, so the route is decided by a sewer map and a camera survey rather than by preference. Order both before the design is fixed. A full plans application adds a decision period, and a sewer close to the footings may also need Thames Water's agreement.

Floor area matters for a different reason. In Merton, a permission for any new dwelling or at least 100 square metres of new-build gross internal area will usually become liable for CIL. A single-storey rear extension normally sits well under that, but a large wrap-around or a two-storey addition on a bigger house can approach it. Measure the gross internal area on the drawings and raise CIL with Merton Council while the design is being fixed. An owner extending their own home can usually claim an exemption, but the claim has to be made before work begins, not after the footings are poured.

Planning and party walls with Merton Council

Whether your extension is permitted development or needs a full planning application depends on the property. Many single-storey rear extensions fall under permitted development, but larger schemes, side extensions, corner plots and anything in a conservation area may require permission from Merton Council. We assess your specific house first and tell you which route applies before any drawings are commissioned, rather than assume.

Every extension also brings building regulations for the foundations, steel and drainage, inspected as the work proceeds. Where your new footings or walls sit against the shared party wall, the Party Wall Act applies too, so you, as building owner, serve the notices your neighbours are entitled to; we supply the drawings and programme they need and keep the whole approvals process moving in one coordinated programme.

Kitchen extensions in Merton

74% of the houses in Merton are terraced. On a terrace the kitchen extension is built out from the back, into the side return where the house has one or across the full rear width, and a steel beam takes the old back wall so the kitchen and the new room become one space. The fit-out is priced on its own page, kitchen renovation in Merton; the build figures are in the table above.

Double storey extensions in Merton

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 Merton often needs planning permission from Merton Council. On the 43% of homes that are terraced, the neighbours' windows usually decide the depth. Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.

• Trial holes to set foundation depth near drains and trees
• Wrap-around extensions and infills
• Building control inspections at foundation, damp course and steel stages

VOA Council Tax stock of properties, March 2025, for all 25 statistical areas in Merton. Counts rounded by the VOA.

Useful next reading for a house extensions project in Merton: RSJ and steel beam installation in Merton, our Merton area guide, wraparound extensions, garage conversions in London, house extensions across London and Bifold vs Sliding Doors.

Trusted House Extensions in Merton

Merton families choose GS Renovation because we manage the extension end to end, from the structural engineer's drawings and building control through to the finished kitchen. One accountable team means tidy working in an occupied home, honest pricing and a build that respects the period fabric, backed by our founder's 30+ years on the tools.

• Permitted development checked before you pay for a planning application
• Garden levels and access made good where the build meets outside
• Materials priced at options, so you choose the finish

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.