Wales cost guide

Extension costs in Wales (2026): prices by area

Updated October 2026Prices include VAT and fees

Quick answerA 20m² single storey rear extension in Wales typically costs £50,500 to £60,500 including VAT. Cardiff prices highest, Swansea and the valleys lower. Rural travel, stone matching and the separate Welsh planning system are the main things that change a quote here.

Typical prices in Wales

Wales Wales, Walesindex 0.96

Single storey rear extension20 m² (5m × 4m)£50,500 to £60,500£2,760/m²
Kitchen extension with bifolds24 m² (6m × 4m), mid spec£67,500 to £81,000£3,060/m²
Double storey rear extension40 m² over two floors£81,500 to £97,500£2,220/m²
Dormer loft conversion2 bedrooms + en-suite£45,500 to £55,500
Velux loft conversion2 rooms£32,500 to £40,000
Garage conversion15 m² single garage£18,500 to £22,500£1,350/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 Wales

Wales has a mix of city suburbs, valley terraces and rural stone houses, and extension costs follow that mix. Cardiff has the busiest market and the highest prices, Newport and the Vale of Glamorgan come close, and Swansea and the South Wales valleys are cheaper. In North and mid Wales, rural sites, slate roofs and stone walls are common, and travel adds to labour costs.

What moves the price in Wales

Valley terraces

The South Wales valleys are lined with stone and brick terraces built on steep hillsides. Gardens are often narrow and sloping, so extensions can need retaining walls and careful access, even though the footprint is small.

Slate and stone

Many Welsh homes have natural slate roofs and stone walls. Matching them on an extension costs more than concrete tiles and block, and in protected areas it may be expected rather than optional.

Rural travel

In mid and North Wales, sites can be a long way from merchants and trades. Travel time and smaller delivery loads on narrow roads feed into the price, even where local labour rates are modest.

Planning and building control in Wales

Planning in Wales is run under Welsh Government rules, which are similar to England's but not identical. Many householder extensions are permitted development, but the limits and conditions differ in places, so don't rely on English guidance. Planning application fees are set separately in Wales. Building Regulations in Wales are also Welsh, with their own energy standards. Check with your local authority before you start.

Prices across Wales

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
CF14	Cardiff	£52,500 to £62,500	£47,000 to £57,000	0.99
SA2	Swansea	£49,000 to £59,000	£44,000 to £54,000	0.93
LL30	Llandudno	£50,500 to £60,500	£45,500 to £55,500	0.96

Cost index for every postcode area in Wales

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
CF	Cardiff	0.99
LD	Llandrindod Wells	0.98
LL	Llandudno	0.96
NP	Newport	0.95
SA	Swansea	0.93

Wales: common questions

How much does an extension cost in Cardiff?

A 20m² single storey rear extension in Cardiff typically costs about £50,500 to £60,500 including VAT, around £2,760 per square metre. Cardiff's northern suburbs tend to sit at the top of the Welsh range.

Are planning rules different in Wales?

Yes. Wales has its own permitted development rules, planning fees and Building Regulations. They are similar to England in principle, but the details differ, so always check with your local authority rather than relying on English guidance.

How much is a loft conversion in Wales?

A dormer loft conversion with two bedrooms and an en-suite typically costs £45,500 to £55,500 including VAT in Wales. A two-room Velux conversion is usually around £32,500 to £40,000.

Does a slate roof make an extension more expensive?

Usually a little. Natural slate costs more than concrete tiles and takes longer to fix. On a flat-roofed rear extension it doesn't apply, which is one reason flat or lean-to roofs are popular on valley terraces.