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 County Londonderry?
In County Londonderry, 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. 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 (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 |
Your quote will depend mainly on:
- Access for materials
- Kitchen and bathroom
- Drainage connection distance
- Heating type
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 County Londonderry?
Approvals for a garden annexe in County Londonderry follow the rules for 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.
At the survey we check your house’s planning history and any restrictions, and tell you which route applies.
What we handle
On a typical garden annexe we handle:
- External cladding or brickwork
- Insulated walls and roof
- Glazed doors and windows
- Foundations and drainage connections
- Kitchenette and shower room
- Planning drawings and application
How long does it take?
Expect 10 to 16 weeks on site. Allow time beforehand for drawings and approvals, usually 3 to 4 months.
Building in County Londonderry
Northern Ireland has many detached and semi-detached homes on generous plots, which suits single-storey rear extensions and garage conversions.
Towns we cover in County Londonderry include Derry, Coleraine, Limavady and Magherafelt.
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
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 garden annexes in County Londonderry
Can it be accessible?
Yes. Level access, wider doors and a wet room can be designed in.
How much does a garden annexe cost in County Londonderry?
In County Londonderry, 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.
Do I need planning permission for a garden annexe in County Londonderry?
In Northern Ireland an annexe with living accommodation needs planning permission and building control approval.
Can an annexe be rented out?
Not without further planning permission, as that would make it a separate dwelling.
Who approves a garden annexe in County Londonderry?
Planning matters in County Londonderry go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.
How long does it take?
Typically 10 to 16 weeks on site.