One of the most common questions we get asked at Brick Builds is "how much will my extension cost?" The honest answer is: it depends — but we can give you real ballpark figures based on what we have actually built across Somerset, Devon and Dorset over the past 17 years. This guide covers the most common extension types with realistic 2026 price ranges.
What Affects the Cost of a House Extension in Somerset?
Before we get to the numbers, it is worth understanding what drives extension costs up or down:
- Size — the larger the floor area, the higher the material and labour cost
- Number of storeys — a double storey extension costs more than single storey but gives twice the space for roughly 60–70% extra cost
- Specification — the quality of windows, doors, roof, and internal finishes varies enormously
- Ground conditions — Somerset clay soil can require deeper, more expensive foundations
- Access — restricted access for a concrete mixer or scaffolding adds cost
- Planning — permitted development is free, a full planning application costs £250–£500 in fees plus any agent costs
- Services — relocating gas, electricity or drainage adds significant cost
2026 Extension Cost Guide — Somerset
| Extension Type | Size | Price Range (supply & fit) |
|---|---|---|
| Single storey rear | 15–20m² | £28,000 – £45,000 |
| Single storey rear | 20–30m² | £40,000 – £65,000 |
| Double storey rear | 20–30m² | £65,000 – £95,000 |
| Side return | 10–15m² | £22,000 – £38,000 |
| Wrap-around (side + rear) | 25–40m² | £75,000 – £120,000 |
| Kitchen extension | 15–25m² | £30,000 – £55,000 |
| Garden room / garden office | 10–20m² | £18,000 – £35,000 |
| Orangery | 15–25m² | £35,000 – £60,000 |
Note:All prices above include foundations, structural work, roofing, external walls, windows and doors, plastering, and first fix electrics and plumbing. They exclude kitchen units, bathroom suites, floor finishes, and decoration — which vary greatly by personal choice.
Do I Need Planning Permission for an Extension in Somerset?
Many extensions in Somerset can be built under Permitted Development rights — meaning no planning application is needed. The main rules are:
- Single storey rear extension: can extend up to 4m on a detached house, 3m on semi or terrace without planning
- Must not exceed 50% of the original garden area
- Height must not exceed 4m (single storey) or the original ridge height (two storey)
- Must be at least 7m from rear boundary (for extensions over 4m on detached)
- Listed buildings and conservation areas always require consent regardless of size
When in doubt, a Pre-Application Enquiry to your local council (Somerset Council, East Devon District, or Dorset Council) costs around £50–£150 and gives you a written answer before you spend money on plans. We can advise you on this as part of your free site visit.
How Long Does a House Extension Take in Somerset?
| Extension Type | Build Time (on site) |
|---|---|
| Single storey rear (small) | 8–12 weeks |
| Single storey rear (large) | 12–16 weeks |
| Double storey | 16–24 weeks |
| Wrap-around | 20–28 weeks |
| Kitchen extension | 10–14 weeks |
Build time starts from when we break ground. Add 4–12 weeks before that for planning (if required) and building regulations approval. We always give you a fixed programme at the start so you know exactly when each stage will be complete.
How to Get an Accurate Extension Quote in Somerset
The only way to get a reliable price is a free site visit. We visit you, look at the existing structure, soil conditions, access, and discuss exactly what you want. We then produce a fixed-price quote — no hidden extras, no surprise bills.
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Why Choose Brick Builds for Your Somerset Extension?
- 17+ years building extensions across Somerset, Devon and Dorset
- Fixed-price contracts — the price we quote is the price you pay
- 500+ completed projects with 5-star reviews
- We handle planning applications and building regulations on your behalf
- Based in Chard — we are genuinely local, not a national franchise
- Full public liability insurance and 10-year structural warranty available