A double-storey extension adds two floors of new space to your house in one build, typically a larger kitchen or living room downstairs with an extra bedroom, bathroom or en-suite above, sharing one set of foundations and one roof.
Looking for a double-storey extension in County Antrim? We organise the whole job, bringing in the trades it needs under one agreement, and you have a single contact. We cover Belfast, Lisburn, Newtownabbey and Carrickfergus, along with villages and suburbs nearby. The rules in Northern Ireland decide what consents are needed, and our guide range of £52,000–£103,000 including VAT gives you a realistic starting point for a budget.
- Guide price
- £52,000–£103,000 inc VAT
- Time on site
- 14–22 weeks on site
- Planning rules
- Northern Ireland
- Price level
- About 14% below the national guide
- Towns listed
- 7
- Survey
- Free, with a written quote
How much does a double-storey extension cost in County Antrim?
Every figure below is a guide for a double-storey extension in County Antrim, inclusive of VAT. Regional pricing for Northern Ireland works out about 14% below the national guide, and the overall span is £52,000–£103,000. The survey costs you nothing, and after it we commit to a firm price for your specification in writing.
| Type of job | What it usually involves | Guide in County Antrim |
|---|---|---|
| Small (15–20m² total) | A compact rear or side extension adding a small room on each floor. | £34,500–£56,000 |
| Typical (30–40m² total) | A larger kitchen or living room below with a double bedroom or en-suite above. | £52,000–£103,000 |
| Large (50m² plus total) | Wide or deep extensions, often with a new bathroom, steelwork and high-spec glazing. | £86,000–£155,000 |
What moves the price up or down:
- Combined floor area across both storeys
- How the new roof joins the existing roof
- Bathrooms, en-suites and plumbing on the upper floor
- Scaffolding duration, access and the level of finishes
Scope of the work
- Insulated cavity walls with brick or render to match the house
- First-floor joists, stud walls and new openings upstairs
- Roof structure tied into the existing roof, tiled to match
- Scaffolding for the full build, erected and inspected
- Electrics, plumbing and heating by qualified trades, with certificates
- Building control inspections and completion certificate
Homes in County Antrim
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.
Terraces suit loft conversions and rear extensions, and many need window and roof renewal. Pebbledashed homes commonly need re-rendering, and detached rural houses often take extensions, porches and driveways.
The north coast and glens are exposed to strong winds, salt and frequent rain, which affects render, roofline and outdoor work.
Planning and building rules in County Antrim
For anyone in County Antrim, the relevant framework is Northern Ireland's. The summary below is general, so we always contact the council about your address before putting a price in writing.
In Northern Ireland, two-storey extensions usually need planning permission from the council.
Building control approval is needed under the Building Regulations (Northern Ireland). There is no Party Wall Act in Northern Ireland.
Rules change and every property is different, so we check the planning history and constraints for your address before we quote.
The four stages
Survey and measure
We begin by looking at the job in person. During the free survey we discuss options, materials and budget for a double-storey extension, and photograph or measure anything the quote needs to reflect.
Price and scope agreed
We turn the survey notes into a written quote. The price is fixed for the specification we agree, and the document sets out materials, scope and payment stages in plain language.
Getting ready
Next comes planning the work itself. We set a start date that suits you, line up the right trades, and make sure any approvals for a double-storey extension are in place before the first day on site.
Finish and handover
The work is carried out to the agreed specification, with floors and furniture protected and the site kept tidy. At the end we clean up, walk through the finished job with you and hand over any certificates.
What you can expect from us
Frequently asked questions
Which postcodes in County Antrim do you cover?
We cover BT1, BT17, BT36 and BT38, along with the rest of County Antrim. If your postcode is not listed, get in touch anyway: our coverage is UK-wide, and we can usually arrange a survey wherever you live. Enter your postcode in the guide-price tool or contact form and we will confirm.
How much does a double-storey extension cost?
A typical double-storey extension of 30–40m² across both floors costs £52,000–£103,000, built to a plastered finish. As a rough guide, allow around £1,400–£2,600 per square metre plus fixed costs for groundworks, scaffolding and fees. The second storey usually costs less per square metre than the first, because foundations and roof are shared. Bathrooms upstairs and a complex roof add most. We confirm a fixed price after the survey.
Do I need planning permission for a two-storey extension?
Most two-storey extensions need planning permission, but it depends on the size, height and position, your home's location, whether it is listed or in a conservation area, and which UK nation you are in. In England, a two-storey rear extension can sometimes be built under permitted development if it is no deeper than 3m and at least 7m from the rear boundary. We check what applies before quoting.
Will the extension affect my neighbours?
A double-storey extension can affect neighbours' light, outlook and privacy, which is why planning departments look closely at height, depth and window positions. Side windows facing neighbours often need obscure glass. Work near a shared wall may also need party wall notices; the Party Wall etc. Act 1996 applies in England and Wales only. We talk through these points early so the design is realistic.
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.
Towns in County Antrim
Below is our list of County Antrim towns for a double-storey extension. If yours isn't shown, we may still cover it, so it is worth asking us directly.