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 Bangor, County Down?
In Bangor, 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. That range is adjusted for Northern Ireland, where domestic building work typically costs around 14% below the national average. 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 |
Your quote will depend mainly on:
- Bathrooms or en-suites on the first floor
- Steel beams where walls are opened up
- Scaffolding and access to the rear
- Total floor area across both floors
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 double-storey extension in Bangor, County Down?
The approval route for Bangor 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.
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.
If the answer is not clear-cut, we can apply for formal confirmation before you commit to the build.
What we handle
Handled as part of most double-storey extensions:
- Opening up at both levels with steel beams
- Building control sign-off
- Brick or block walls, floors and a roof tied into the house
- Structural engineer’s calculations
- Windows, doors and staircase alterations
- Electrics, heating, plumbing and plastering
How long does it take?
Build time is typically 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 Bangor, County Down
Northern Ireland has many detached and semi-detached homes on generous plots, which suits single-storey rear extensions and garage conversions.
Our Bangor coverage includes postcode districts BT19 and BT20, and we also work in nearby places such as Newtownards, Carrickfergus and Newtownabbey.
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
Design and fixed quote
Drawings, structural calculations and an itemised, fixed price for the agreed specification.
- 03
Permissions sorted
Applications, building control and neighbour arrangements, all before the start date.
- 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 Bangor, County Down
How much does a double-storey extension cost in Bangor?
In Bangor, 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.
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.
Do I need planning permission for a double-storey extension in Bangor?
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.
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.
Who approves a double-storey extension in Bangor?
Planning matters in Bangor go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.