First-floor extensions in Belmont (Greater London)

The basics for Belmont (Greater London) at a glance.

Postcode districts: SM2
County / area: Greater London, England
Price region: London
Guide price: £30,000–£43,500 (£2,160–£3,120 per m²)
Approval route: It may be permitted development if it goes no more than 3 m beyond the original rear wall (counting any single-storey part) and stays 7 m from the rear boundary; otherwise it needs planning permission.
Nearest towns: Sutton (0.5 miles), Banstead (1.5 miles), Cheam (1.5 miles)
First visit: Free, no obligation

About a first-floor extension

A first-floor extension is a new upstairs room built on top of an existing single-storey part of your house, such as a rear kitchen extension, a utility or a side annexe. It adds a bedroom, bathroom or study without enlarging the footprint. Whether it works depends mainly on whether the walls and foundations below can carry the extra load.

Around Belmont (Greater London) we also work in Sutton, Banstead and Cheam, and across the rest of Greater London. Postcode district in and near Belmont (Greater London): SM2.

What it costs in Belmont (Greater London)

Guide prices for first-floor extensions in London are around £2,160–£3,120 per m² of new floor space, including VAT. For a typical project with 4 m × 3.5 m of new first-floor space (14 m²), that's roughly £30,000–£43,500. Steelwork for wide openings is the item most likely to move the figure; we'll know once the engineer has designed it.

Spec	Per m²	4 m × 3.5 m of new first-floor space (14 m²)
Essential	£1,990–£2,870 per m²	£28,000–£40,000
Standard	£2,160–£3,120 per m²	£30,000–£43,500
Premium	£2,590–£3,740 per m²	£36,500–£52,500

Planning and building regulations in Belmont (Greater London)

In England, adding a first floor turns a single-storey extension into one of more than one storey. To be permitted development, the extension as a whole must go no more than 3 m beyond the rear wall of the original house and stay at least 7 m from the rear boundary, with matching materials and roof pitch. Over a side extension it always needs planning permission, costing £548 (or £575 for applications made from 8 December 2026).

Approval in England: Householder planning application: £548 (or £575 for applications made from 8 December 2026). Lawful development certificate: £274 (about £288 for applications from 8 December 2026). Councils should decide householder applications within 8 weeks of validation.

Building regulations: Building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end.

Design points for Belmont (Greater London) homes

Matching the roofline

A first-floor extension often changes how the back or side of the house looks more than the original single storey did. Matching the main roof pitch and materials, and keeping the ridge below the main ridge, usually gives the best result and is expected for permitted development in England.

Replacing the flat roof

The existing roof usually comes off and is replaced by a new first-floor structure. The room below is exposed for a short time, so we plan temporary weatherproofing and sequence the work to keep the kitchen or living room usable for as long as possible.

How we'd run your project

Start at your house
We come to your home in Belmont (Greater London), measure up, check the ground floor walls and roof structure, and note anything near the boundaries.
Plans, then approval
Measured survey, design, then the right approval route for your house. We explain each step before we take it.
Fixed price in writing
With approved drawings and calculations, we give you a fixed build price and a programme you can plan around.
Build and hand over
We manage the build from groundworks to decoration-ready finish and hand over with the completion paperwork.

Questions about first-floor extensions in Belmont (Greater London)

How long does a first-floor extension take?

Allow 4 to 8 weeks for survey and design, then the approval period (councils should decide householder applications within 8 weeks of validation), then 4 to 8 weeks of technical design, which can overlap. The build itself usually takes 14 to 20 weeks, longer for large or complex designs.

Do I need planning permission for a first-floor extension in Belmont (Greater London)?

Belmont (Greater London) is in England, so England planning rules apply. It may be permitted development if it goes no more than 3 m beyond the original rear wall (counting any single-storey part) and stays 7 m from the rear boundary; otherwise it needs planning permission. If in doubt, a lawful development certificate or a planning application gives you certainty before you build.

How much does a first-floor extension cost in Belmont (Greater London)?

Our guide for London, which covers Belmont (Greater London), is £2,160–£3,120 per m² including VAT. A typical project with 4 m × 3.5 m of new first-floor space (14 m²) comes to about £30,000–£43,500. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

What happens to the room below while the first floor is built?

The old roof is removed, so the room below is exposed for a short period. We fit temporary weather protection, plan the work so the roof comes off only when the new structure is ready, and agree with you which rooms will be out of use and for roughly how long.

Will the first-floor extension match my house?

It should, and in England matching materials and roof pitch is a condition of permitted development. We match brick, tile, mortar colour and window style where we can, and tell you at the design stage if an exact brick match is not available, so you can choose between the closest match and render or cladding.

Nearby

Close to Belmont (Greater London)? We work across the area, including:

Other extensions in Belmont (Greater London)

All two-storey extension services in Belmont (Greater London) · First-floor extensions across Greater London

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