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 Downpatrick?
In Downpatrick, 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. We start from a UK-wide guide and adjust it for Northern Ireland, where labour and materials are typically about 14% below average. 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 main things that change the cost:
- Glazing: sliding and bifold doors cost more than French doors
- Roof type and the size of any lantern or roof windows
- Kitchen, flooring and finishes, which we can include or leave to you
- Floor area and the length of new wall
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 Downpatrick?
Here is how the rules work for a single-storey extension 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.
At the survey we check your house’s planning history and any restrictions, and tell you which route applies.
What we handle
What we take care of:
- Building control inspections and completion certificate
- Structural calculations for steels and lintels
- Cavity walls, insulation and roof to current building regulations
- First and second fix electrics, heating and plastering
- Foundations, drainage and any build-over agreement
- Doors, windows and roof glazing installed
How long does it take?
Expect 10 to 14 weeks on site for a typical rear extension, after approvals. Allow time beforehand for drawings and approvals, usually 6 to 12 weeks.
Building in Downpatrick
Across Northern Ireland, bungalows and chalet bungalows are common, so loft conversions and rear extensions are popular projects.
Downpatrick sits in County Down, about 20 miles south-east of Belfast. We cover the whole of Downpatrick, including postcodes BT30.
How it works
- 01
Survey and brief
We visit, discuss your ideas and budget, and survey the property or site at no cost.
- 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
Construction and completion
We build, put right any snags and hand over the building control certificate.
Questions about single-storey extensions in Downpatrick
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.
Do I need planning permission for a single-storey extension in Downpatrick?
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.
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.
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.
Do you build single-storey extensions in Downpatrick?
Yes. We build single-storey extensions across Downpatrick, including postcodes BT30. Every project starts with a free home visit.
How much does a single-storey extension cost in Downpatrick?
In Downpatrick, 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.