What is a double-storey extension?
A double-storey extension (also called a two-storey extension) adds rooms on both the ground and first floor in one build. It typically gives a larger kitchen or living space downstairs and an extra bedroom or bathroom above.
How much does a double-storey extension cost in Somerset?
In Somerset, a double-storey extension typically costs £1,700–£2,550 per m² of floor area (both floors), including VAT at 20% (standard rate). For a typical 36 m² project that is roughly £61,000–£92,000. Prices in the South West sit near the national average for this kind of work, and the range for Somerset reflects that. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (25 m²) | £42,500–£64,000 |
| Typical project (36 m²) | £61,000–£92,000 |
| Larger project (50 m²) | £85,000–£127,500 |
| Rate per m² | £1,700–£2,550 |
The biggest cost drivers are:
- Roof design and how it joins the existing roof
- Scaffolding and access to the rear
- Brick matching and external finishes
- Bathrooms or en-suites on the first floor
Your exact price depends on the survey and drawings. The guide price tool gives a quick range in the meantime.
Do you need planning permission for a double-storey extension in Somerset?
Before anything is built in Somerset, we confirm which approvals apply in England. In England an extension of more than one storey can only be permitted development at the rear, no more than 3 metres deep and at least 7 metres from the rear boundary, with matching materials and any upper side windows obscure-glazed. Most double-storey extensions therefore go through a householder planning application.
Where work involves a shared wall, building on the boundary, or digging foundations within 3 metres of a neighbour’s building and deeper than its foundations (or within 6 metres for deeper work), the Party Wall etc. Act 1996 applies and notices must be served before work starts.
If the answer is not clear-cut, we can apply for formal confirmation before you commit to the build.
What we handle
From survey to sign-off, the job normally involves:
- Foundations, drainage and scaffolding
- Design drawings and planning application
- Brick or block walls, floors and a roof tied into the house
- Windows, doors and staircase alterations
- Structural engineer’s calculations
- Opening up at both levels with steel beams
How long does it take?
Allow 14 to 20 weeks on site, after planning and building control approval. Before that, surveys, drawings and approvals usually take 3 to 4 months, longer if the council asks for changes.
Building in Somerset
The South West mixes stone and render cottages with post-war and newer estates, and local materials matter more here when matching an extension.
Towns we cover in Somerset include Mendip, Bath, Weston-super-Mare, Taunton, Yeovil and Bridgwater.
How it works
- 01
Visit and measured survey
A free visit to understand the project, check access and take measurements.
- 02
Design and pricing
Design options, then a fixed quote based on the chosen drawings and specification.
- 03
Permissions sorted
Applications, building control and neighbour arrangements, all before the start date.
- 04
Build and handover
Work follows the agreed programme, with inspections along the way and a completion certificate at the end.
Questions about double-storey extensions in Somerset
Will the first floor need a new staircase?
Not normally. The new rooms are reached from the existing landing, though a doorway or short corridor may need to be formed.
How much does a double-storey extension cost in Somerset?
In Somerset, a double-storey extension typically costs £1,700–£2,550 per m² of floor area (both floors), including VAT at 20% (standard rate). A typical 36 m² project comes to roughly £61,000–£92,000. Your fixed price depends on the survey and drawings.
Is a double-storey extension cheaper per square metre?
Usually yes. You pay for one set of foundations and one roof but get two floors of space, so the cost per square metre is often lower than a single-storey extension.
Who approves a double-storey extension in Somerset?
Planning matters in Somerset go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.
How close can it be to my neighbour?
Councils look at loss of light and outlook for neighbours. Many apply a 45-degree guideline from the nearest neighbouring window. We design to the council’s published guidance to give the application the best chance.