Extension Cost in South West (2026)
A extension in South West typically costs between £33,300 and £49,900 - roughly 4% above the UK average. Higher local labour rates and strong demand are the main factors driving prices up.
£33,300–£49,900
Typical range
£41,600
Average cost
+4%
vs national avg
10–16 weeks
Typical duration
Free, no obligation. Quotes from vetted tradespeople in South West.
Important: Building Regulations approval is required for all house extensions. Most single-storey rear extensions up to 6m (detached) or 3m (semi/terrace) fall under Permitted Development, but you should always check with your local council before starting work.
South West extension prices
Prices below reflect the typical cost of an extension in South West, including materials and labour.
| Type | Details | South West range | South West avg |
|---|---|---|---|
| Single-storey rear | 3m x 4m basic build, plastered and decorated | £33,300 – £49,900 | £41,600 |
| Single-storey side | Infill or wraparound, converting dead space | £29,900 – £44,900 | £37,400 |
| Double-storey rear | Two floors, extra bedroom and living space | £58,200 – £87,400 | £72,800 |
All prices include materials and labour. Based on contractor submissions and market data, April 2026.
What affects extension costs in South West
Extension costs are heavily influenced by local build rates - the cost per square metre for structural work. In South West, builders typically charge £42–£60 per hour for general construction labour, which affects the per-square-metre rate for your build.
The South West includes everything from Bristol's urban terraces to rural Devon and Cornwall cottages. Older stone-built properties are common in more rural areas and can be more complex to work on. The type of property you are extending matters. A straightforward rear extension on a detached house is simpler than extending a mid-terrace or a property on a slope.
Foundation costs can vary significantly. Rock and slate subsoil is common in parts of Devon and Cornwall, which can make excavation more expensive.
Planning and Building Regulations fees are set nationally, but if your extension requires full planning permission rather than falling under Permitted Development, the design and application process adds time and cost. The South West has extensive Areas of Outstanding Natural Beauty and national parks that can restrict certain types of development.
How South West compares
South West extension costs compared to other UK regions and the national average.
| Region | Average cost | vs national avg |
|---|---|---|
| South East | £45,000 | +13% |
| East of England | £42,600 | +7% |
| South WestYou are here | £41,600 | +4% |
| National average | £40,000 | - |
| Midlands | £40,000 | Average |
| Yorkshire | £37,400 | -6% |
How to get your extension for less in South West
Use Permitted Development rights
If your extension qualifies under Permitted Development, you skip the full planning application - saving £200 to £500 in fees and potentially months of waiting. Check with your local council before assuming you need planning permission.
Get a fixed-price contract
Extensions are complex and costs can escalate. Insist on a fixed-price contract from your South West builder that covers all structural work, roofing, plastering, electrics, and plumbing. Vague quotes lead to expensive surprises.
Build during quieter months
Builders in South West are typically busiest from April to September. Starting your build in autumn or winter can sometimes get you a better price, though weather delays are more likely.
Frequently asked questions
How much does a house extension cost in South West?
Do I need planning permission for an extension in South West?
How long does it take to build an extension in South West?
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