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 Coleraine?
In Coleraine, 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. The guide for Coleraine reflects typical costs in Northern Ireland, roughly 14% below the UK-wide figure. 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 |
Your quote will depend mainly on:
- Ground conditions and foundation depth
- Glazing: sliding and bifold doors cost more than French doors
- Roof type and the size of any lantern or roof windows
- How much of the existing house is opened up
Your exact price depends on the survey and drawings. The guide price tool gives a quick range in the meantime.
Do you need planning permission for a single-storey extension in Coleraine?
The approval route for Coleraine is set by planning law in 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:
- Structural calculations for steels and lintels
- Knock-through to the existing house with steel beams
- Doors, windows and roof glazing installed
- Cavity walls, insulation and roof to current building regulations
- Building control inspections and completion certificate
- Foundations, drainage and any build-over agreement
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 Coleraine
Northern Ireland has many detached and semi-detached homes on generous plots, which suits single-storey rear extensions and garage conversions.
We work across Coleraine and neighbouring areas such as Limavady, Ballymena and Magherafelt. Postcodes we cover in Coleraine include BT51 and BT52.
How it works
- 01
Free visit
We look at the property, talk through what you want and measure up. There is no charge and no obligation.
- 02
Drawings and written quote
We prepare the design and give you a written, itemised quote with inclusions and exclusions.
- 03
Approvals
Planning or permitted development confirmation, building regulations and any party wall matters.
- 04
Build and handover
Work follows the agreed programme, with inspections along the way and a completion certificate at the end.
Questions about single-storey extensions in Coleraine
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.
How long does a single-storey extension take?
Once approvals are in place, a typical rear extension takes 10 to 14 weeks on site. Design and approvals usually take another 6 to 12 weeks beforehand, depending on whether a planning application is needed.
How much does a single-storey extension cost in Coleraine?
In Coleraine, 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.
Do you build single-storey extensions in Coleraine?
Yes. We build single-storey extensions across Coleraine, including postcodes BT51 and BT52. Every project starts with a free home visit.
Do I need planning permission for a single-storey extension in Coleraine?
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.
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.