First-floor extensions in Belfast
For a first-floor extension in Belfast, the first questions are always the same: how big, which approvals, and what it will cost. This page answers all three for County Antrim.
What we'd confirm first for a project in Belfast.
- Postcode districts
- BT1, BT2, BT3, BT7, BT9, BT11 and nearby districts
- County / area
- County Antrim, Northern Ireland
- Price region
- Northern Ireland
- Guide price
- £22,000–£32,000 (£1,580–£2,290 per m²)
- Approval route
- It may be permitted development if it goes no more than 3 m beyond the original rear wall and stays 7 m from the rear boundary.
- Nearest towns
- Castlereagh (2.3 miles), Newtownabbey (4.4 miles), Holywood (5 miles)
- First visit
- Free, no obligation
About a first-floor extension
A first-floor extension is a new upstairs room built on top of an existing single-storey part of your house, such as a rear kitchen extension, a utility or a side annexe. It adds a bedroom, bathroom or study without enlarging the footprint. Whether it works depends mainly on whether the walls and foundations below can carry the extra load.
Around Belfast we also work in Castlereagh, Newtownabbey and Holywood, and across the rest of County Antrim. Postcode districts in and near Belfast: BT1, BT2, BT3, BT7, BT9, BT11 and nearby districts.
What it costs in Belfast
A guide price for Belfast: around £22,000–£32,000 for 4 m × 3.5 m of new first-floor space (14 m²). That works out at £1,580–£2,290 per m² of new floor space, including VAT at 20%. Professional fees for drawings and the structural engineer are listed separately on our prices page.
| Spec | Per m² | 4 m × 3.5 m of new first-floor space (14 m²) |
|---|---|---|
| Essential | £1,460–£2,100 per m² | £20,500–£29,500 |
| Standard | £1,580–£2,290 per m² | £22,000–£32,000 |
| Premium | £1,900–£2,750 per m² | £26,500–£38,500 |
Planning and building control in Belfast
In Northern Ireland, a first floor over a rear extension can be permitted development if the extension goes no more than 3 m beyond the original rear wall and stays at least 7 m from the rear boundary, with height, materials and roof pitch conditions. Over a side extension, or beyond these limits, a planning application costs £347 per dwelling.
Approval in Northern Ireland: Planning application for works to a house: £347. Councils aim to decide local applications within an average of 15 weeks; many take longer.
Building control: Building control approval from the local council under the Building Regulations (Northern Ireland), using the Technical Booklets.
Design points for Belfast homes
Replacing the flat roof
The existing roof usually comes off and is replaced by a new first-floor structure. The room below is exposed for a short time, so we plan temporary weatherproofing and sequence the work to keep the kitchen or living room usable for as long as possible.
Escape and fire safety
A new first-floor bedroom needs an escape window with a clear opening of at least 0.33 m², at least 450 mm wide and 450 mm high, with the bottom no more than 1,100 mm above the floor, unless there is a protected route to the stairs.
How we'd run your project
Start at your house
We come to your home in Belfast, measure up, check the ground floor walls and roof structure, and note anything near the boundaries.
Get it approved
Once you're happy with the design we submit it to the council for Belfast and deal with any questions from the planning officer.
Detail and price
Construction drawings, engineer's calculations and building control sign-off, then a written fixed price for the build.
On site
One project lead runs the job, keeps you updated and arranges inspections at each stage until completion.
Questions about first-floor extensions in Belfast
Do I need planning permission for a first-floor extension in Belfast?
Belfast is in Northern Ireland. It may be permitted development if it goes no more than 3 m beyond the original rear wall and stays 7 m from the rear boundary.
How long does a first-floor extension take?
Allow 4 to 8 weeks for survey and design, then the approval period (councils aim to decide local applications within an average of 15 weeks; many take longer), then 4 to 8 weeks of technical design, which can overlap. The build itself usually takes 14 to 20 weeks, longer for large or complex designs.
Who handles building control for a project in Belfast?
We handle it as part of the project. What's needed in Northern Ireland: building control approval from the local council under the Building Regulations (Northern Ireland), using the Technical Booklets. We prepare the drawings and the engineer's calculations, book the inspections and pass you the completion paperwork at the end.
Can I build on top of my existing single-storey extension?
Often yes, but only after the structure has been checked. Foundations, walls and lintels built for one storey may not carry two. We dig trial holes, look for the original building control approval and ask the structural engineer to confirm what can stay, what needs strengthening and what must be rebuilt.
What happens to the room below while the first floor is built?
The old roof is removed, so the room below is exposed for a short period. We fit temporary weather protection, plan the work so the roof comes off only when the new structure is ready, and agree with you which rooms will be out of use and for roughly how long.
Nearby
Close to Belfast? We work across the area, including:
Other extensions in Belfast
- Rear
- Side
- Wraparound
- Part two-storey
- Over a garage
- Semi-detached
- Detached
- Kitchen and bedrooms
- Bedroom and en-suite
All two-storey extension services in Belfast · First-floor extensions across County Antrim
Tell us about your house in Belfast and we'll call you back to arrange a free, no-obligation visit.