A single-storey extension is a new ground-floor room built onto your house, usually at the rear or side, with its own foundations, walls and roof, creating a bigger kitchen, living space or bedroom without moving home.
Homeowners in Belfast usually consider a single-storey extension for one of a few reasons: something has worn out, the house no longer suits the way they live, or they are getting it ready to sell. We visit, agree a specification and put a fixed price in writing. Most jobs like this take 10–16 weeks on site, and we work across County Antrim, including Castlereagh, Newtownabbey and Lisburn.
- Guide price
- £30,000–£64,000 inc VAT
- Time on site
- 10–16 weeks on site
- Postcodes
- BT1, BT2, BT6, BT7 and BT12
- Planning rules
- Northern Ireland
- Local area
- County Antrim
- Survey
- Free, with a written quote
How much does a single-storey extension cost in Belfast?
To help you plan, we show what a single-storey extension typically costs in Belfast instead of holding figures back for a sales call. The range is £30,000–£64,000 with VAT, using rates in Northern Ireland that are about 14% below the national guide. A free survey then fixes your actual price.
| Type of job | What it usually involves | Guide in Belfast |
|---|---|---|
| Small extension (8–12m²) | A modest rear or side extension, such as a utility room or a slightly larger kitchen. | £19,000–£34,500 |
| Typical rear extension (15–25m²) | A kitchen-diner or family room with bifold doors and a rooflight or lantern. | £30,000–£64,000 |
| Large or wrap-around (30m² plus) | A wrap-around or wide rear extension, often with structural steelwork into the house. | £60,000–£112,000 |
The main things that change the figure:
- Floor area, shape and number of corners
- Roof type, rooflights, lanterns and the amount of glazing
- Ground conditions, foundation depth and drains to divert
- Finishes, kitchen, flooring and heating specification
What do you get?
- Groundworks, foundations and below-ground drainage
- Flat or pitched roof, with rooflights or a lantern if specified
- Steel beams to open into the existing house
- Windows and external doors, including bifolds if chosen
- Plastering, screed floor and internal doors
- Building control inspections and completion certificate
Local housing and a single-storey extension
Belfast has long rows of red-brick Victorian terraces, Edwardian villas in the north and south of the city and large post-war estates, while towns such as Ballymena, Antrim, Larne and Carrickfergus mix terraces, semis and newer developments. Dark basalt appears in older rural buildings, and pebbledash or roughcast is a very common finish.
The north coast and glens are exposed to strong winds, salt and frequent rain, which affects render, roofline and outdoor work.
So when we survey a Belfast property for a single-storey extension, the first step is working out how it was built and what has been changed since.
Do you need permission in Belfast?
Each UK nation sets its own consent rules, and Belfast is in Northern Ireland. What follows is a plain summary; we check the specifics for your property with the council before pricing anything.
In Northern Ireland, permitted development allows many single-storey rear extensions, typically up to 3 m deep on attached houses and 4 m on detached houses, within height and garden-coverage limits. Conservation areas, listed buildings and side extensions are more restricted.
Building control approval under the Building Regulations (Northern Ireland) is needed for extensions. Northern Ireland has no Party Wall Act, so boundary work is agreed with neighbours directly.
Rules change and every property is different, so we check the planning history and constraints for your address before we quote.
From survey to handover
Free site survey
First, someone visits your home in Belfast to see the space, take measurements and note anything that could affect the work, such as access or the condition of what is there. There is no charge for this visit.
Your fixed price
You get the price in writing, itemised so you can see where the money goes. As long as the specification stays the same, that is the price you pay for a single-storey extension.
Booking the work
We handle the paperwork side: checking whether planning permission or building control approval is needed, submitting applications where they are, and scheduling the trades and materials around your dates.
On site to finish
The job proceeds in the order set out in the programme, with dust and debris kept under control. Finally we tidy away, inspect the work together and pass the finished project over to you with its paperwork.
How we work
Single-storey extensions in Belfast: questions
Do you cover Castlereagh, Newtownabbey and Lisburn?
Yes. As well as Belfast, we cover Castlereagh, Newtownabbey and Lisburn and the rest of County Antrim. Our coverage is UK-wide, so the process is the same wherever you are: a free site survey, a quote in writing that fixes the price for the agreed scope, and one point of contact while the work is planned and carried out.
How long does a single-storey extension take to build?
A single-storey extension usually takes 10–16 weeks on site, from digging foundations to final plastering. Bad weather, deep foundations or a complex roof can add time. Before work starts, allow several weeks for drawings, structural calculations and building control approval, and longer if planning permission is needed. We give you a stage-by-stage programme with your quote so you know what happens each week.
Who do I deal with during the job?
One point of contact manages your project from survey to handover. They schedule the trades working under our contract, keep you updated on progress, and are the person to call with any question. You don't need to coordinate builders, electricians or decorators separately, because that is part of what we do.
What is the Party Wall Act and does it apply to me?
The Party Wall etc. Act 1996 applies in England and Wales only. In England and Wales, it requires you to give notice to neighbours before certain work on or near a shared wall, such as digging foundations within 3m of their building and deeper than its footings. Neighbours can agree or appoint a surveyor. Scotland and Northern Ireland have no equivalent Act, though general rights still apply. We identify whether notices are needed during the survey.
Is a flat roof or a pitched roof better on an extension?
A flat roof is quicker to build and usually costs less, gives a clean modern look and works well with a roof lantern. A pitched roof matches the main house, sheds water faster and allows a vaulted ceiling, but it costs more and its height can affect neighbours. Modern flat roofs in EPDM rubber or GRP last well when properly detailed. Planning rules on height can also decide the choice.
Near Belfast
Belfast and its BT1, BT2, BT6 and BT7 postcodes are part of our coverage. Homeowners in Castlereagh, Newtownabbey and Lisburn can also book a free survey with us and receive a written price for their job.