Northern Ireland cost guide

Extension costs in Northern Ireland (2026): local prices

Updated October 2026Prices include VAT and fees

Quick answerA 20m² single storey rear extension in Northern Ireland typically costs £47,500 to £56,500 including VAT, the lowest of any UK region on our index. South Belfast and North Down price highest. Lower labour costs drive the difference, while materials cost much the same as in Great Britain.

Typical prices in Northern Ireland

Northern Ireland Northern Ireland, Northern Irelandindex 0.90

Single storey rear extension20 m² (5m × 4m)£47,500 to £56,500£2,570/m²
Kitchen extension with bifolds24 m² (6m × 4m), mid spec£63,500 to £76,000£2,870/m²
Double storey rear extension40 m² over two floors£76,000 to £91,000£2,070/m²
Dormer loft conversion2 bedrooms + en-suite£42,500 to £52,000
Velux loft conversion2 rooms£30,500 to £37,000
Garage conversion15 m² single garage£17,500 to £21,000£1,270/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 Northern Ireland

Northern Ireland is the most affordable part of the UK to extend a home, mainly because labour rates are lower. Prices are highest in south Belfast, around the Malone Road and Stranmillis, and in North Down towns such as Holywood and Bangor. Rural extensions on detached houses are common across the province, often larger than urban projects, with more space for single storey kitchen and family rooms.

What moves the price in Northern Ireland

Lower labour costs

Trades in Northern Ireland generally charge less than in Great Britain, which is the main reason extensions cost less. Materials are a similar price, and some are shipped from Great Britain, so the saving narrows on high-spec projects.

Rural detached houses

Many projects are on detached rural homes with large plots, so bigger extensions with generous glazing are common. Longer drainage runs, septic tank or treatment plant work and access tracks can add cost on rural sites.

Weather and exposure

Wet, windy weather is common, especially near the coast. Builders allow for lost days and specify robust render, roofing and window details, which is worth paying for.

Planning and building control in Northern Ireland

Northern Ireland has its own planning system, run by its councils under Department for Infrastructure rules, and its own permitted development limits. Building control is handled by council building control departments under Northern Ireland's Building Regulations. The principles are similar to England, but the details and fees differ, so check with your council before you finalise a design.

Prices across Northern Ireland

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
BT9	Belfast	£47,500 to £56,500	£42,500 to £52,000	0.90
BT20	Belfast	£47,500 to £56,500	£42,500 to £52,000	0.90
BT47	Belfast	£47,500 to £56,500	£42,500 to £52,000	0.90

Cost index for every postcode area in Northern Ireland

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
BT	Belfast	0.90

Northern Ireland: common questions

How much does an extension cost in Belfast?

A 20m² single storey rear extension in Belfast typically costs about £47,500 to £56,500 including VAT, around £2,570 per square metre. South Belfast tends to sit at the top of that range.

Is it cheaper to build in Northern Ireland?

Usually, yes. Labour costs less than in Great Britain, which brings totals down. Materials are similar in price, so the saving is smaller on high-spec jobs with expensive glazing or kitchens.

Do planning rules differ in Northern Ireland?

Yes. Northern Ireland has its own planning system, permitted development rules, fees and Building Regulations. Your council's planning and building control teams can confirm what your project needs.

How much is a garage conversion in Northern Ireland?

Converting a 15m² single garage typically costs £17,500 to £21,000 including VAT. You will usually need building control approval for the new habitable room, even if planning permission is not needed.