Structural Alterations Merton

GS Renovation carries out structural alterations throughout Merton, working on the Victorian and Edwardian terraces of Wimbledon, the interwar terraces and semis of Mitcham and Morden, and the flats and larger suburban homes across the borough. Our founder's 30+ years on the tools has covered new openings, replacement joists, supported openings and underpinning, each designed by a structural engineer and signed off by building control.

In Merton, a simple new opening starts from £1,500, and underpinning a single elevation typically costs £6,000 to £21,000 (indicative London ranges, MyBuilder and Checkatrade, 2026). GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Merton.

How the job runs

1. Free site survey at your Merton address and an itemised quote.
2. The engineer we appoint designs the work, and it is registered with Merton Council building control or an approved inspector. On a shared wall you serve the party wall notice as building owner; we supply the drawings.
3. Props and any trial holes first, then the opening, joists or underpinning in the engineer's sequence.
4. Building control inspects each stage before it is covered, then issues the completion certificate.

Structural work for Merton's period homes

The typical Merton terrace has a rear closet wing and a side return, and much of our structural work is about widening the link between the original house and those spaces. Forming a new opening into a side-return extension, or a wider doorway between the closet wing and kitchen, means the masonry above has to be caught on a lintel or steel beam bearing onto padstones. An engineer sizes every element first.

Older properties near Mitcham Common and Morden Hall Park often need more than a new opening. We replace decayed or undersized floor joists, form supported openings where a wall is only partly removed, and where foundations have moved we underpin in carefully sequenced bays. Each of these is designed to a structural engineer's specification and propped and staged so the building stays stable throughout.

Housing in Merton

By the valuation list's count, Merton holds about 87,830 homes, 58% houses and 42% flats; by age, 26% were built before 1919, 37% between the wars and 36% since 1945. Underpinning the party wall of a terrace in Merton needs a notice to the neighbour, and 43% of homes here are terraced.

Checking listings and access before altering a Merton home

Merton Council states there are currently around 250 statutory listed buildings in Merton, and it also publishes a local list, Locally listed buildings in Merton, dated November 2021. Check both before a structural design is drawn, because they answer different questions. A statutory listing brings listed building consent into play for internal alterations as well as external ones, and that consent shapes the engineering. A local listing does not require listed building consent, but planners can take it into account where an outside change needs permission. Neither status is obvious from the street.

The second check in Merton is who else the work reaches. 42% of homes in Merton are flats, and in a flat an alteration can extend into rooms you do not own. A floor trimmed for a new stair, or a wall replaced by a beam, may need props standing in the flat below, and the engineer may need to see the ceiling void from underneath. Ask that neighbour for access at survey stage and agree dates in writing before the steel is ordered, so the propping plan does not depend on a door that stays shut.

Engineering and consents across Merton

Any alteration that changes how loads travel through the building is notifiable under the Building Regulations, and Merton Council's building control inspects the works at the key stages and issues the completion certificate. We book those inspections, keep the engineer's calculations on site and make sure padstones, beam bearings and connections match the approved design before anything is closed up.

Where an opening, a new bearing or underpinning affects a wall shared with the adjoining house, the Party Wall Act applies and you, as building owner, serve notice on the neighbour before starting; we supply the drawings and programme it needs. This matters on Merton's tightly packed terraced streets in SW19 and CR4, where the party wall is doing structural work for both homes. Internal alterations like these need building control, not planning permission; the exception is a listed home, where they need listed building consent. Changes to the outside may need planning, especially in a conservation area.

• Chimney breast removal and support to the stack above
• Temporary works, propping and needling
• Reinstatement, plastering and finishing after structural works

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

Once the structural alterations work in Merton is scoped, people usually go on to read home renovation in Merton, our Merton area guide, a main building contractor in London, underpinning in London, structural alterations across London and Subsidence in London.

The GS Renovation Difference in Merton

For structural alterations, Merton homeowners get one team managing the engineer we appoint, the propping and staged construction, and building control's inspections through to sign-off, all under a single point of contact. We keep the site clean and the house liveable while we work, and we bring our founder's 30+ years of experience.

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.