Kitchen Extensions Merton

A kitchen extension in Merton starts from the house type. Terraced houses make up 43% of the borough's homes against 15% semi-detached or detached. On a terrace the brief is a side return infill or a rear box that pulls the kitchen into the garden; a semi or detached house has the width for a wraparound. Before anything is drawn we check whether a public sewer runs near the back wall, because in Merton that decides which building control route you take and how early the paperwork has to start.

In Merton, a rear kitchen extension of about 30 square metres typically costs £45,000 to £97,500 excluding VAT, or £60,000 to £100,000 for a side return (indicative London ranges, 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 foundations and steel, we build the room and fit the kitchen, and a registered electrician certifies the electrics.

Side returns and rear boxes on Merton terraces and semis

On a Merton terrace the side return is where the extra kitchen space comes from. The narrow strip beside the back addition is filled in, the old outrigger wall is opened up, and the kitchen, dining space and garden door end up in one room. With terraced houses at 43% of the borough's homes, this is a common shape of extension here, and it is the one that needs most care over the neighbour's wall, the boundary and the light reaching the next house.

Permitted development sets the outer limit for a simple rear box. Nationally a single storey rear extension can go three metres beyond the original rear wall of a terrace or semi, or four metres on a detached house, and no higher than four metres. Merton semis and detached houses, 15% of homes, have the width for an L shaped wraparound, which joins a side extension to the rear one and in most cases takes the project out of permitted development and into a planning application.

Housing in Merton

Merton counts roughly 87,830 homes for Council Tax; 26% are older than 1919, 37% interwar and 36% post-war, with 42% flats and 58% houses. A terrace kitchen extension in Merton starts in a narrow side return, and 43% of homes here are terraced.

Flats, John Innes and designated land in Merton

If you own a flat in Merton, you start from planning permission, not permitted development. The householder extension rules apply to houses only, and flats are 42% of the borough's homes, so this affects a large group of owners. A ground floor flat with a garden needs a planning application and, on a leasehold, the freeholder's written consent as well. We price the build once those are in hand, and we keep the construction within the approved footprint and materials.

Designated land narrows the options further. Every side extension on land such as a conservation area needs householder permission, which catches a wraparound on a semi inside one. In the John Innes Merton Park and Wilton Crescent conservation areas, four Article 4 directions also bring changes such as a roof slope or a porch that fronts the highway under control. Merton's fast track householder decision runs up to 30 days from validation outside a conservation area and up to 46 days inside one, so we plan the start date around that.

Why a nearby sewer changes the Merton building control route

In Merton the position of the public sewer decides your building control route. If the extension comes within 3 metres of a Thames Water sewer, a full plans submission has to be made before work starts, and a building notice is not available. Older terraces often have a shared run behind the houses, so we find the manhole covers and trace the run on the first visit. Building over or close to a public sewer can also need Thames Water's own agreement, which the owner or designer arranges.

The full plans route has its own timing. Merton issues a decision within five weeks, or up to two months if agreed, from the date the first payment is received, and work may begin once 48 hours notice of commencement has been given. Merton's example inspection stages for an extension include the foundation excavation, the oversite, and the new walls with the below ground drainpipes. We leave each stage open until it has been seen, then close it up and move on.

Steel, roof lights and the new kitchen in a Merton extension

Opening the back of the house is the structural heart of a Merton kitchen extension. Merton's full plans application needs structural calculations where the work removes load bearing walls or forms new openings, so the structural engineer we appoint produces them before submission. Where the steel bears on a party wall, or new footings sit close to a neighbour's and go deeper, the Party Wall etc. Act applies and you, as building owner, serve the notices. We then prop, cut the opening and set the steel on its padstones.

Light and services come next. A deep side return can leave the middle of the house dark, so roof lights over the old passage and a wide glazed opening to the garden do the work that the lost window used to do. We run the kitchen fit in the same programme. Drainage and first fix go in while the floor is open and the steel stays visible until it has been inspected. Then the screed goes down, and the units, worktops and appliances go in once plaster has dried.

• Sliding, bifold and steel-framed glazed doors to the garden
• Foundations, drainage and slab with the kitchen services cast in
• Flat roofs with rooflights or a roof lantern over the kitchen

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

Next steps that tend to follow kitchen extensions in Merton: kitchen renovation in Merton, our Merton area guide, fitting the kitchen itself, party wall notices for a kitchen extension, our London kitchen extensions page and Renovating a 1930s Semi.

The GS Renovation Difference in Merton

You get one team from the first opening in the back wall to the last kitchen door. We price from a visit, set out the sequence on paper, and work to the approved drawings and the structural engineer's design. The inspector's stages are built into the programme rather than squeezed in, and the kitchen trades follow the builders without a gap for you to manage. Our founder brings more than three decades of hands-on building to the site, and you deal with the same people throughout.

• Drains surveyed by camera before the footprint is fixed
• Boiler flue, soil pipe and gully moved off the rear wall in the right order
• Registered in England, Companies House no. 14611254

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.