What is a garden annexe?
A garden annexe is a single-storey building in the garden with its own living space, bathroom and often a kitchenette, used by relatives, older children or guests. Unlike a garden room, it is built as habitable accommodation with foundations, insulation and services.
How much does a garden annexe cost in Belfast?
In Belfast, a garden annexe typically costs £1,550–£2,400 per m² of floor area, including VAT at 20% (standard rate). For a typical 35 m² project that is roughly £54,000–£84,000. Prices across Northern Ireland are typically 14% below the UK average for this kind of work, which is reflected in the range for Belfast. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (24 m²) | £37,000–£57,500 |
| Typical project (35 m²) | £54,000–£84,000 |
| Larger project (49 m²) | £76,000–£117,500 |
| Rate per m² | £1,550–£2,400 |
What moves the price most:
- Heating type
- Size and layout
- Kitchen and bathroom
- Cladding and finishes
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 garden annexe in Belfast?
Here is how the rules work for a garden annexe in Northern Ireland. In Northern Ireland an annexe with living accommodation needs planning permission and building control approval.
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 garden annexe we handle:
- Building control sign-off
- Insulated walls and roof
- Glazed doors and windows
- Foundations and drainage connections
- Electrics and heating
- External cladding or brickwork
How long does it take?
The build itself usually takes 10 to 16 weeks on site. Allow time beforehand for drawings and approvals, usually 3 to 4 months.
Building in Belfast
Northern Ireland has many detached and semi-detached homes on generous plots, which suits single-storey rear extensions and garage conversions.
If your home is in Belfast or close by in Newtownabbey, Lisburn and Newtownards, a free home visit is the first step.
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 sign-off
We run the build to a written programme and hand over the completion certificate.
Questions about garden annexes in Belfast
How much does a garden annexe cost in Belfast?
In Belfast, a garden annexe typically costs £1,550–£2,400 per m² of floor area, including VAT at 20% (standard rate). A typical 35 m² project comes to roughly £54,000–£84,000. Your fixed price depends on the survey and drawings.
Can an annexe be rented out?
Not without further planning permission, as that would make it a separate dwelling.
How long does it take?
Typically 10 to 16 weeks on site.
Do I need planning permission for a garden annexe in Belfast?
In Northern Ireland an annexe with living accommodation needs planning permission and building control approval.
Do you build garden annexes in Belfast?
Yes. We build garden annexes across Belfast, including postcodes BT1, BT2, BT3 and BT4. Every project starts with a free home visit.
Can it be accessible?
Yes. Level access, wider doors and a wet room can be designed in.