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 Cardiff?
In Cardiff, a garden annexe typically costs £1,650–£2,600 per m² of floor area, including VAT at 20% (standard rate). For a typical 35 m² project that is roughly £58,000–£91,000. The guide for Cardiff reflects typical costs in Wales, roughly 8% below the UK-wide figure. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (24 m²) | £39,500–£62,500 |
| Typical project (35 m²) | £58,000–£91,000 |
| Larger project (49 m²) | £81,000–£127,500 |
| Rate per m² | £1,650–£2,600 |
What moves the price most:
- Kitchen and bathroom
- Size and layout
- Heating type
- Drainage connection distance
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 Cardiff?
Whether you need planning permission depends on your house and its location in Wales. In Wales an annexe with sleeping accommodation usually needs planning permission; outbuildings under permitted development must be incidental to the house.
Building regulations in Wales are set by the Welsh Government. Approval comes from the council’s building control service or a registered building control approver, with inspections during the work and a completion certificate at the end.
We check this for your address before design work starts, so there are no surprises later.
What we handle
Handled as part of most garden annexes:
- Kitchenette and shower room
- Glazed doors and windows
- Foundations and drainage connections
- Building control sign-off
- Insulated walls and roof
- Planning drawings and application
How long does it take?
Allow 10 to 16 weeks on site. Before that, surveys, drawings and approvals usually take 3 to 4 months, longer if the council asks for changes.
Building in Cardiff
Terraced houses in Welsh towns often have narrow plots, which suits rear and side return extensions and rear dormers.
We work across Cardiff and neighbouring areas such as Penarth, Caerphilly and Barry. Postcodes we cover in Cardiff include CF10, CF11, CF14 and CF15.
How it works
- 01
Visit and measured survey
A free visit to understand the project, check access and take measurements.
- 02
Design and pricing
Design options, then a fixed quote based on the chosen drawings and specification.
- 03
Approvals
Planning or permitted development confirmation, building regulations and any party wall matters.
- 04
Construction and completion
We build, put right any snags and hand over the building control certificate.
Questions about garden annexes in Cardiff
How long does it take?
Typically 10 to 16 weeks on site.
How much does a garden annexe cost in Cardiff?
In Cardiff, a garden annexe typically costs £1,650–£2,600 per m² of floor area, including VAT at 20% (standard rate). A typical 35 m² project comes to roughly £58,000–£91,000. Your fixed price depends on the survey and drawings.
Who approves a garden annexe in Cardiff?
Planning matters in Cardiff go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.
Does it need building regulations?
Yes, as it contains sleeping accommodation and services.
Will council tax apply?
Annexes can be banded separately, though discounts or exemptions apply in some cases when occupied by family. Check with your council.
Do I need planning permission for a garden annexe in Cardiff?
In Wales an annexe with sleeping accommodation usually needs planning permission; outbuildings under permitted development must be incidental to the house.