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.
An annexe used as accommodation ancillary to the main house usually needs planning permission, and it must not become a separate dwelling without further approval.
What we handle
- Planning drawings and application
- Foundations and drainage connections
- Insulated walls and roof
- Kitchenette and shower room
- Electrics and heating
- Glazed doors and windows
- External cladding or brickwork
- Building control sign-off
Options to consider
Granny annexe
Step-free access and wider doors for older relatives.
Teenager or guest annexe
Bedroom, shower room and lounge.
Office and studio
Workspace with a WC.
Brick or timber clad
Match the house or choose a contemporary finish.
How much does a garden annexe cost?
A garden annexe typically costs £1,800–£2,800 per m² of floor area across the UK, including VAT at 20% (standard rate). A typical 35 m² project comes to roughly £63,000–£98,000. Build time is usually 10 to 16 weeks on site. Design, structural calculations and council fees are extra.
| Region | Guide range (per m² of floor area) |
|---|---|
| London | £2,350–£3,650 |
| South East | £2,000–£3,150 |
| East of England | £1,900–£2,950 |
| South West | £1,850–£2,850 |
| West Midlands | £1,750–£2,700 |
| East Midlands | £1,700–£2,650 |
| North West | £1,700–£2,650 |
| Yorkshire and the Humber | £1,650–£2,600 |
| North East | £1,600–£2,500 |
| Wales | £1,650–£2,600 |
| Scotland | £1,750–£2,700 |
| Northern Ireland | £1,550–£2,400 |
What changes the price:
- Size and layout
- Kitchen and bathroom
- Drainage connection distance
- Access for materials
- Cladding and finishes
- Heating type
Use the guide price tool for a figure based on your measurements, or see all guide prices.
Do I need planning permission?
England
In England an annexe used as living accommodation usually needs planning permission. Outbuildings built under permitted development must be incidental to the house, such as a gym or office, not a bedroom.
Wales
In Wales an annexe with sleeping accommodation usually needs planning permission; outbuildings under permitted development must be incidental to the house.
Scotland
In Scotland an annexe with living accommodation needs planning permission and a building warrant.
Northern Ireland
In Northern Ireland an annexe with living accommodation needs planning permission and building control approval.
Even when planning permission is not needed, building regulations approval (a building warrant in Scotland) usually is. We make the applications and book the inspections.
How long does it take?
Typically 10 to 16 weeks on site. Surveys, design and approvals usually take 3 to 4 months beforehand.
How it works
- 01
Free visit
We look at the property, discuss what you want and measure up.
- 02
Design and fixed quote
Drawings, calculations and an itemised price for the agreed specification.
- 03
Approvals
Planning or permitted development, building regulations and neighbour matters.
- 04
Build and sign-off
Built to a written programme, with a completion certificate at the end.
Garden annexes: questions and answers
Does a garden annexe need planning permission?
Usually yes if it is used as living accommodation. Outbuildings under permitted development must be incidental to the house, such as a gym or office, not bedrooms.
Can an annexe be rented out?
Not without further planning permission, as that would make it a separate dwelling.
Does it need building regulations?
Yes, as it contains sleeping accommodation and services.
How long does it take?
Typically 10 to 16 weeks on site.
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.
Can it be accessible?
Yes. Level access, wider doors and a wet room can be designed in.