First-floor extensions in Street

Useful details for planning a first-floor extension in Street.

Postcode districts: BA6, BA16, TA10 and TA11
County / area: Somerset, England
Price region: South West England
Guide price: £26,000–£37,500 (£1,850–£2,680 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: Wells (7 miles), Shepton Mallet (9.5 miles), Bridgwater (11.4 miles)
Distance to Bath: about 23.8 miles
First visit: Free, no obligation

About a first-floor extension

A first-floor extension suits you if your house already has a single-storey extension and you need more space upstairs. You get a structural check of the existing walls and foundations, a design that ties the new floor into the house, the approvals your nation needs, building regulations approval and the build, managed by us and carried out by vetted teams working under S&K.

We cover Street (BA6, BA16, TA10 and TA11) and the places around it, including Wells (7.0 miles), Shepton Mallet (9.5 miles) and Bridgwater.

What it costs in Street

A guide price for Street: around £26,000–£37,500 for 4 m × 3.5 m of new first-floor space (14 m²). That works out at £1,850–£2,680 per m² of new floor space, including VAT at 20%. 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	£1,710–£2,460 per m²	£24,000–£34,500
Standard	£1,850–£2,680 per m²	£26,000–£37,500
Premium	£2,220–£3,210 per m²	£31,000–£45,000

Planning and building regulations in Street

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 Street 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.

Tying into the house

The new floor and walls must line up with the existing first floor, often through a new opening in the rear wall above the old one. Floor levels, the position of upstairs windows and the existing roof all affect where the opening can go, so we survey both floors carefully.

How we'd run your project

Understand the brief
At your home in Street we agree what you need: bedroom count, bathroom, kitchen space, and how much garden you want to keep.
Design and approvals
We draw the extension and check it against the rules for England, then apply for planning permission or a certificate of lawfulness, whichever fits.
Detail and price
Construction drawings, engineer's calculations and building control sign-off, then a written fixed price for the build.
Build it
The new structure goes up first, then we open into the house, finish inside and get the completion certificate.

Questions about first-floor extensions in Street

How much does a first-floor extension cost in Street?

Our guide for South West England, which covers Street, is £1,850–£2,680 per m² including VAT. A typical project with 4 m × 3.5 m of new first-floor space (14 m²) comes to about £26,000–£37,500. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

Who handles building regulations for a project in Street?

We handle it as part of the project. What's needed in England: building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end. We prepare the drawings and the engineer's calculations, book the inspections and pass you the completion paperwork at the end.

Which postcodes do you cover around Street?

We cover Street (BA6, BA16, TA10 and TA11) and nearby places including Wells, Shepton Mallet and Bridgwater, plus the rest of Somerset. The first site visit is free.

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.

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.

Nearby

The same service in neighbouring towns:

Other extensions in Street

All two-storey extension services in Street · First-floor extensions across Somerset

Send us your postcode and a few details. We'll get back to you to arrange a visit and talk through your options.