What is a double-storey extension?
A double-storey extension (also called a two-storey extension) adds rooms on both the ground and first floor in one build. It typically gives a larger kitchen or living space downstairs and an extra bedroom or bathroom above.
How much does a double-storey extension cost in Carrickfergus?
In Carrickfergus, a double-storey extension typically costs £1,400–£2,150 per m² of floor area (both floors), including VAT at 20% (standard rate). For a typical 36 m² project that is roughly £50,500–£77,500. The guide for Carrickfergus 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 (25 m²) | £35,000–£54,000 |
| Typical project (36 m²) | £50,500–£77,500 |
| Larger project (50 m²) | £70,000–£107,500 |
| Rate per m² | £1,400–£2,150 |
What moves the price most:
- Steel beams where walls are opened up
- Total floor area across both floors
- Brick matching and external finishes
- Scaffolding and access to the rear
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 double-storey extension in Carrickfergus?
The approval route for Carrickfergus is set by planning law in Northern Ireland. In Northern Ireland an extension of more than one storey can be permitted development at the rear if it projects no more than 3 metres and is at least 7 metres from the rear boundary. Two-storey side extensions, and any in a conservation area, need planning permission.
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.
Our first visit includes a check of your planning history, so you know the route before paying for drawings.
What we handle
On a typical double-storey extension we handle:
- Opening up at both levels with steel beams
- Windows, doors and staircase alterations
- Design drawings and planning application
- Building control sign-off
- Brick or block walls, floors and a roof tied into the house
- Structural engineer’s calculations
How long does it take?
Expect 14 to 20 weeks on site, after planning and building control approval. Allow time beforehand for drawings and approvals, usually 3 to 4 months.
Building in Carrickfergus
Across Northern Ireland, bungalows and chalet bungalows are common, so loft conversions and rear extensions are popular projects.
Carrickfergus sits in County Antrim, about 10 miles north-east of Belfast. We cover the whole of Carrickfergus, including postcodes BT38.
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 double-storey extensions in Carrickfergus
Will the first floor need a new staircase?
Not normally. The new rooms are reached from the existing landing, though a doorway or short corridor may need to be formed.
What drawings do I need?
Planning drawings for the application, then more detailed building regulations drawings and structural calculations for building control. We prepare both.
How much does a double-storey extension cost in Carrickfergus?
In Carrickfergus, a double-storey extension typically costs £1,400–£2,150 per m² of floor area (both floors), including VAT at 20% (standard rate). A typical 36 m² project comes to roughly £50,500–£77,500. Your fixed price depends on the survey and drawings.
Do I need planning permission for a double-storey extension in Carrickfergus?
In Northern Ireland an extension of more than one storey can be permitted development at the rear if it projects no more than 3 metres and is at least 7 metres from the rear boundary. Two-storey side extensions, and any in a conservation area, need planning permission.
Do you build double-storey extensions in Carrickfergus?
Yes. We build double-storey extensions across Carrickfergus, including postcodes BT38. Every project starts with a free home visit.
Can I live at home during the work?
Most families stay put. The shell is built first and the house is opened up late in the job, so disruption inside is limited to a few weeks.