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 County Londonderry?
In County Londonderry, 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. Prices across Northern Ireland are typically 14% below the UK average for this kind of work, which is reflected in the range for County Londonderry. 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:
- Floor area and the length of new wall
- Ground conditions and foundation depth
- Glazing: sliding and bifold doors cost more than French doors
- How much of the existing house is opened up
For a figure based on your own measurements, try the guide price tool, then book a free home visit for a fixed quote.
Do you need planning permission for a single-storey extension in County Londonderry?
Approvals for a single-storey extension in County Londonderry 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.
In Northern Ireland building control approval comes from the council, usually through a full plans application or a building notice, with inspections during the work and a completion certificate at the end.
If the answer is not clear-cut, we can apply for formal confirmation before you commit to the build.
What we handle
On a typical single-storey extension we handle:
- Cavity walls, insulation and roof to current building regulations
- Building control inspections and completion certificate
- Measured survey and design drawings
- First and second fix electrics, heating and plastering
- Doors, windows and roof glazing installed
- 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. Design and approvals come first and typically take 6 to 12 weeks, depending on the approval route.
Building in County Londonderry
Across Northern Ireland, bungalows and chalet bungalows are common, so loft conversions and rear extensions are popular projects.
Towns we cover in County Londonderry include Derry, Coleraine, Limavady and Magherafelt.
How it works
- 01
Visit and measured survey
A free visit to understand the project, check access and take measurements.
- 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
Construction and completion
We build, put right any snags and hand over the building control certificate.
Questions about single-storey extensions in County Londonderry
How much does a single-storey extension cost in County Londonderry?
In County Londonderry, 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 County Londonderry?
Yes. We build single-storey extensions across County Londonderry, including postcodes BT28, BT45, BT46, BT47 and BT48. Every project starts with a free home visit.
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.
Do I need planning permission for a single-storey extension in County Londonderry?
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.