What is a single-storey extension?
A single-storey extension is a ground-floor addition, usually at the rear of a house, that enlarges a kitchen, living or dining space. Most are built with cavity walls on concrete foundations and finished with a flat roof and roof lantern or a pitched tiled roof.
How much does a single-storey extension cost in Larne?
In Larne, a single-storey extension typically costs £1,700–£2,500 per m² of floor area, including VAT at 20% (standard rate). For a typical 20 m² project that is roughly £34,000–£50,000. Building costs in Northern Ireland run about 14% below the UK average, and the figures for Larne are adjusted to reflect that. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (14 m²) | £24,000–£35,000 |
| Typical project (20 m²) | £34,000–£50,000 |
| Larger project (28 m²) | £47,500–£70,000 |
| Rate per m² | £1,700–£2,500 |
The biggest cost drivers are:
- How much of the existing house is opened up
- Glazing: sliding and bifold doors cost more than French doors
- Floor area and the length of new wall
- Roof type and the size of any lantern or roof windows
A guide range is only a starting point: the guide price tool gives an instant figure for your size, and a free survey turns it into a fixed quote.
Do you need planning permission for a single-storey extension in Larne?
Approvals for a single-storey extension in Larne follow the rules for Northern Ireland. In Northern Ireland the Planning (General Permitted Development) Order (Northern Ireland) 2015 allows single-storey rear extensions of up to 3 metres on attached houses and 4 metres on detached houses, no higher than 4 metres, with eaves no higher than 3 metres within 2 metres of a boundary. Houses with removed rights need planning permission, listed buildings need consent, and in conservation areas extensions must stay single-storey and must not come forward of the front or side walls.
Northern Ireland has no Party Wall Act. Work on shared walls relies on agreement with the neighbour and common law, so we agree the arrangements in writing before work starts.
We check this for your address before design work starts, so there are no surprises later.
What we handle
On a typical single-storey extension we handle:
- Doors, windows and roof glazing installed
- Cavity walls, insulation and roof to current building regulations
- Building control inspections and completion certificate
- First and second fix electrics, heating and plastering
- Foundations, drainage and any build-over agreement
- Structural calculations for steels and lintels
How long does it take?
Expect 10 to 14 weeks on site for a typical rear extension, after approvals. Before that, surveys, drawings and approvals usually take 6 to 12 weeks, longer if the council asks for changes.
Building in Larne
Across Northern Ireland, bungalows and chalet bungalows are common, so loft conversions and rear extensions are popular projects.
Our Larne coverage includes postcode districts BT40, and we also work in nearby places such as Carrickfergus, Newtownabbey and Bangor.
How it works
- 01
Survey and brief
We visit, discuss your ideas and budget, and survey the property or site at no cost.
- 02
Design and fixed quote
Drawings, structural calculations and an itemised, fixed price for the agreed specification.
- 03
Approvals
Planning or permitted development confirmation, building regulations and any party wall matters.
- 04
Build and sign-off
We run the build to a written programme and hand over the completion certificate.
Questions about single-storey extensions in Larne
Can I stay in the house during the build?
Usually yes. We build the shell before opening up the back wall, so the house stays weathertight for most of the job. There will be a few weeks when the kitchen or back room is out of use.
Is VAT charged on an extension?
Yes. Building work on an existing home is standard-rated, so VAT at 20% applies. Our guide prices include it.
How much does a single-storey extension cost in Larne?
In Larne, a single-storey extension typically costs £1,700–£2,500 per m² of floor area, including VAT at 20% (standard rate). A typical 20 m² project comes to roughly £34,000–£50,000. Your fixed price depends on the survey and drawings.
How long does a single-storey extension take in Larne?
Typically 10 to 14 weeks on site for a typical rear extension, after approvals. Design and approvals beforehand usually take 6 to 12 weeks.
Do I need planning permission for a single-storey extension in Larne?
In Northern Ireland the Planning (General Permitted Development) Order (Northern Ireland) 2015 allows single-storey rear extensions of up to 3 metres on attached houses and 4 metres on detached houses, no higher than 4 metres, with eaves no higher than 3 metres within 2 metres of a boundary. Houses with removed rights need planning permission, listed buildings need consent, and in conservation areas extensions must stay single-storey and must not come forward of the front or side walls.
What is a build-over agreement?
If a public sewer runs within 3 metres of the extension, the water company normally has to agree to the work before it starts. We check sewer records during design and apply where needed.