the South West cost guide

Extension costs in the South West (2026): prices by area

Updated October 2026Prices include VAT and fees

Quick answerA 20m² single storey rear extension in the South West typically costs £55,500 to £66,000 including VAT. Bath and Bristol price highest, Plymouth and Torbay lower. Stone matching, conservation rules and longer travel to rural sites are what usually move a South West quote.

Typical prices in the South West

the South West the South West, South Westindex 1.05

Single storey rear extension20 m² (5m × 4m)£55,500 to £66,000£3,010/m²
Kitchen extension with bifolds24 m² (6m × 4m), mid spec£73,500 to £88,000£3,330/m²
Double storey rear extension40 m² over two floors£89,000 to £106,500£2,420/m²
Dormer loft conversion2 bedrooms + en-suite£49,500 to £60,500
Velux loft conversion2 rooms£35,500 to £43,500
Garage conversion15 m² single garage£20,500 to £24,500£1,480/m²

All prices include 20% VAT, professional fees and statutory planning fees. Kitchen extension includes a mid-range kitchen, bifolds and a roof lantern.

Price my exact project

Building in the South West

The South West has some of the UK's most varied building traditions, from Bath stone and Cotswold limestone to Cornish granite and Devon cob. That matters for extensions, because many councils expect new work to sit comfortably next to the old. Bristol and Bath have busy, higher priced markets, while Plymouth, Torbay and much of Somerset are closer to the national middle. Rural jobs in Cornwall and Devon can add travel and delivery time.

What moves the price in the South West

Natural stone

Extensions in Bath, the Cotswolds edge and many villages are often expected to use natural stone or a convincing reconstituted stone. Stonework is slower and dearer than block and render, and skilled masons are in demand, so this can be the single biggest difference between two similar quotes.

Rural sites and travel

Outside the cities, sites can be a long drive from builders' merchants and trades. Narrow lanes limit lorry access, so deliveries come in smaller loads. Travel time is priced into labour, which keeps rural prices up even where wages are lower.

Coastal exposure

Houses near the coast face wind-driven rain and salt air. Builders and building control may specify better render systems, stainless fixings and more robust windows, which add a little to the materials bill but last far longer.

Planning and building control in the South West

English permitted development rules apply, but the South West has large areas of national park, national landscape and conservation area where rights are reduced or design is scrutinised more closely. Bath is a World Heritage Site with strong controls in the city. Every extension needs Building Regulations approval. Speak to your council's planning team early if you live in a protected area or an older stone property.

Prices across the South West

A 20m² single storey rear extension and a two-bedroom dormer loft with an en-suite, priced for each example postcode. All figures include VAT and fees.

Postcode	Area	Single storey, 20m²	Dormer loft	Index
BS7	Bristol	£57,500 to £69,000	£51,500 to £63,000	1.09
EX4	Exeter	£55,000 to £65,500	£49,000 to £60,000	1.04
BA2	Bath	£58,500 to £70,000	£52,500 to £64,000	1.11

Cost index for every postcode area in the South West

Our index against the West Midlands base of 1.00. Higher means dearer. Enter a full postcode in the checker for district-level detail where we have it.

Area	Main town	Index
BA	Bath	1.11
BH	Bournemouth	1.07
BS	Bristol	1.09
DT	Dorchester	1.05
EX	Exeter	1.04
GL	Gloucester	1.05
PL	Plymouth	0.99
SN	Swindon	1.03
SP	Salisbury	1.07
TA	Taunton	1.01
TQ	Torquay	1.00
TR	Truro	1.03

the South West: common questions

How much does an extension cost in the South West?

A 20m² single storey rear extension typically costs £55,500 to £66,000 including VAT. Bath and Bristol sit at the top of the range, especially where natural stone is required. Plymouth, Torbay and Taunton are usually lower.

Does using Bath stone or natural stone cost more?

Yes. Natural stone walling is slower to lay and the material costs more than brick or block with render. On a typical single storey extension it can add several thousand pounds, so ask your builder to price stone and render options separately.

How much is a kitchen extension in Bristol?

A 24m² kitchen extension with bifold doors and a roof lantern at mid spec typically costs £73,500 to £88,000 including VAT across the South West, and Bristol tends to land in the upper half of that range.

Do I need planning for a loft conversion in the South West?

Many loft conversions are permitted development, within volume limits of 40m³ for terraced houses and 50m³ for semis and detached houses. In national parks and conservation areas those rights are often removed. A dormer loft with two bedrooms and an en-suite typically costs £49,500 to £60,500.