First-floor extensions in Wealdstone

Before you start in Wealdstone, here's what applies.

Postcode districts: HA3
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: Harrow Weald (0.8 miles), Harrow (1.5 miles), Hatch End (1.7 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 Wealdstone we also work in Harrow Weald, Harrow and Hatch End, and across the rest of Greater London. Postcode district in and near Wealdstone: HA3.

What it costs in Wealdstone

A guide price for Wealdstone: around £30,000–£43,500 for 4 m × 3.5 m of new first-floor space (14 m²). That works out at £2,160–£3,120 per m² of new floor space, including VAT at 20%. These are guides, not quotes. Ground conditions, steelwork and access can move the figure either way.

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 Wealdstone

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 Wealdstone 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.

Escape and fire safety

A new first-floor bedroom needs an escape window with a clear opening of at least 0.33 m², at least 450 mm wide and 450 mm high, with the bottom no more than 1,100 mm above the floor, unless there is a protected route to the stairs.

How we'd run your project

Free site visit
We visit your home in Wealdstone, look at the structure, access and boundaries, and talk through what you want the new rooms to do.
Get it approved
Once you're happy with the design we submit it to the council for Wealdstone and deal with any questions from the planning officer.
Fixed price in writing
With approved drawings and calculations, we give you a fixed build price and a programme you can plan around.
Build
Foundations, walls, floor, roof, windows, then first and second fix. We break through into the house as late as we can.

Questions about first-floor extensions in Wealdstone

Do I need planning permission for a first-floor extension in Wealdstone?

Wealdstone 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 Wealdstone?

Our guide for London, which covers Wealdstone, 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.

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.

Can I build on top of my existing single-storey extension?

Often yes, but only after the structure has been checked. Foundations, walls and lintels built for one storey may not carry two. We dig trial holes, look for the original building control approval and ask the structural engineer to confirm what can stay, what needs strengthening and what must be rebuilt.

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.

Nearby

Close to Wealdstone? We work across the area, including:

Other extensions in Wealdstone

All two-storey extension services in Wealdstone · First-floor extensions across Greater London

The quickest next step is a visit. We'll look at your house in Wealdstone and give you an honest view of the options.