Two-storey extensions for detached houses in Keynsham

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

Postcode districts: BS31
County / area: Somerset, England
Price region: South West England
Guide price: £88,500–£119,000 (£2,110–£2,830 per m²)
Approval route: Depends on position: a two-storey rear extension may be permitted development (3 m deep, 7 m from the rear boundary); a two-storey side extension needs planning permission.
Nearest towns: Kingswood (2.7 miles), Whitchurch (Bristol) (2.8 miles), Publow (3.1 miles)
Distance to Bath: about 6.5 miles
First visit: Free, no obligation

About a two-storey extension for a detached house

A two-storey extension for a detached house is a two-floor addition to the side, rear or both of a house that stands on its own plot. Detached houses often have room on more than one side, so there is more choice of layout and fewer shared-wall issues. The design still needs to respect boundaries, neighbours' windows and the look of the house.

We cover Keynsham (BS31) and the places around it, including Kingswood (2.7 miles), Whitchurch (Bristol) (2.8 miles) and Publow.

What it costs in Keynsham

Guide prices for two-storey extensions for detached houses in South West England are around £2,110–£2,830 per m² of new floor space, including VAT. For a typical project with a 3 m × 7 m footprint on two floors (42 m² of new floor space), that's roughly £88,500–£119,000. The fastest way to a firmer number is a free site visit, after which we price the design stage in writing.

Spec	Per m²	A 3 m × 7 m footprint on two floors (42 m² of new floor space)
Essential	£1,940–£2,610 per m²	£81,500–£109,500
Standard	£2,110–£2,830 per m²	£88,500–£119,000
Premium	£2,530–£3,400 per m²	£106,500–£143,000

Planning and building regulations in Keynsham

In England, a two-storey rear extension on a detached house can be permitted development within 3 m of the original rear wall and at least 7 m from the rear boundary, with matching roof pitch and materials, outside protected areas. Any two-storey side or wraparound extension needs planning permission, costing £548 (or £575 for applications made from 8 December 2026), with a decision due within 8 weeks of validation.

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 Keynsham homes

Larger spans and steelwork

Bigger extensions often mean wider openings and longer spans, which need more steel and sometimes a steel frame. The engineer designs these early, because the size of the steel affects ceiling heights, floor depths and the cost.

Keeping it subordinate

Large detached houses can take a large extension, but councils still expect it to look secondary to the main house. A lower ridge, a modest set-back at the front and matching materials keep the proportions right, even on a wide plot.

How we'd run your project

Start at your house
We come to your home in Keynsham, 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 sign-off
Vetted teams working under S&K build the extension, and we arrange the building control completion certificate at the end.

Questions about two-storey extensions for detached houses in Keynsham

Which postcodes do you cover around Keynsham?

We cover Keynsham (BS31) and nearby places including Kingswood, Whitchurch (Bristol) and Publow, plus the rest of Somerset. The first site visit is free.

Do I need planning permission for a two-storey extension for a detached house in Keynsham?

Keynsham is in England, so England planning rules apply. Depends on position: a two-storey rear extension may be permitted development (3 m deep, 7 m from the rear boundary); a two-storey side extension needs planning permission. If in doubt, a lawful development certificate or a planning application gives you certainty before you build.

Who handles building regulations for a project in Keynsham?

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.

How big an extension can a detached house take?

It depends on the plot, the boundaries and local design policy rather than a fixed limit. Under permitted development in England, extensions must not cover more than 50% of the land around the original house. With planning permission, the council judges size on proportion, neighbours and the character of the area.

Can I extend a detached house on both sides?

Sometimes. With planning permission, a council may accept extensions on both sides if the house stays well proportioned and keeps gaps to the boundaries. It is more common to extend on one side and the rear, or with a wraparound. We look at the plot as a whole before suggesting more than one extension.

Nearby

Nearby towns we cover for two-storey extensions for detached houses:

Other extensions in Keynsham

All two-storey extension services in Keynsham · Two-storey extensions for detached houses across Somerset

Ready to talk it through? Call us or send the form and we'll arrange a visit to your home in Keynsham.