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 Hampstead?
In Hampstead, a garden annexe typically costs £2,350–£3,650 per m² of floor area, including VAT at 20% (standard rate). For a typical 35 m² project that is roughly £82,000–£128,000. The guide for Hampstead reflects typical costs in London, roughly 30% above the UK-wide figure. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (24 m²) | £56,500–£87,500 |
| Typical project (35 m²) | £82,000–£128,000 |
| Larger project (49 m²) | £115,000–£179,000 |
| Rate per m² | £2,350–£3,650 |
What moves the price most:
- Drainage connection distance
- Kitchen and bathroom
- Heating type
- Access for materials
Your exact price depends on the survey and drawings. The guide price tool gives a quick range in the meantime.
Do you need planning permission for a garden annexe in Hampstead?
Before anything is built in Hampstead, we confirm which approvals apply in 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.
Building regulations approval comes from the council’s building control service or a registered building control approver. The work is inspected at key stages, such as foundations, drainage and insulation, and a completion certificate is issued at the end.
We check this for your address before design work starts, so there are no surprises later.
What we handle
On a typical garden annexe we handle:
- Building control sign-off
- External cladding or brickwork
- Insulated walls and roof
- Foundations and drainage connections
- Planning drawings and application
- Electrics and heating
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 Hampstead
Many London boroughs have conservation areas and detailed design guides, so early design advice saves time at the planning stage.
Hampstead sits in Greater London, about 4 miles north-west of central London. We cover the whole of Hampstead, including postcodes NW3.
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 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 Hampstead
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.
Do you build garden annexes in Hampstead?
Yes. We build garden annexes across Hampstead, including postcodes NW3. Every project starts with a free home visit.
How long does it take?
Typically 10 to 16 weeks on site.
Can an annexe be rented out?
Not without further planning permission, as that would make it a separate dwelling.
How much does a garden annexe cost in Hampstead?
In Hampstead, a garden annexe typically costs £2,350–£3,650 per m² of floor area, including VAT at 20% (standard rate). A typical 35 m² project comes to roughly £82,000–£128,000. Your fixed price depends on the survey and drawings.