Planning permission: needed for a dwelling, no shortcuts
This is the part people most often get wrong: an ancillary garden room that supports the main house - a home office, a gym, a spare guest room used occasionally - can often be permitted development. An annexe designed and used as a self-contained dwelling, with its own kitchen and a lockable, separate living arrangement, generally cannot. It needs full planning permission.
Local authorities look at whether the annexe is genuinely ancillary to the main house or functions as an independent dwelling - things like a separate postal address, letting it out, or removing all practical dependency on the main house all push it towards needing consent. We assess this honestly at the outset rather than quoting a build that gets refused or enforced against later.
Building regulations, drainage and services
An annexe with a kitchen and bathroom falls fully under building regulations regardless of the planning route - structure, fire safety, means of escape, ventilation, thermal performance and drainage all have to be signed off. Foul drainage is usually the deciding factor on layout: we assess whether the annexe can gravity-connect to the existing system or needs a pumped or macerator connection, and price that properly rather than as an afterthought.
Hot water, ventilation extraction from the bathroom and kitchen, and a compliant means of escape (usually a second door or an openable window meeting size and location rules) all get designed in from the start.
- Full planning permission required where the annexe is a self-contained dwelling
- Building regulations sign-off covers structure, fire safety, drainage and ventilation
- Foul drainage: gravity connection where levels allow, pumped/macerator where they don't
- Council tax: a self-contained annexe can attract a separate council tax band, though many qualify for a discount when occupied by a dependent relative - check with your local authority
Cost and what's included
A garden annexe with a kitchenette and shower room, fully insulated and finished, typically starts from around £45,000 to £65,000 depending on size and specification, reflecting the additional drainage, ventilation and fire-safety work over a standard garden room. This includes groundworks, drainage connection, insulation, certified electrics, heating and a full interior fit-out.
We'd rather give you that real number at the start than a headline price that doesn't include the drainage run or the planning application, both of which are unavoidable on a genuine annexe.
Where we build garden annexes
We design and build annexes across Mid Sussex, the wider Sussex counties, Surrey and Kent, working with your local planning authority from the earliest sketch stage since annexe rules vary district to district.
- Haywards Heath
- Cuckfield
- Lindfield
- Burgess Hill
- Horsham
- East Grinstead
- Reigate
- Oxted
- Tunbridge Wells
- Sevenoaks
Garden annexe questions
- Do I need planning permission for a garden annexe?
- If it's a self-contained dwelling with its own kitchen and independent living arrangement, yes - full planning permission is required. Ancillary use without a kitchen can sometimes fall under permitted development, but we check this against your specific plans and local authority before quoting.
- Can an annexe be used as a separate rental?
- Only with planning permission granted for that use, and it will usually be considered a separate dwelling for council tax and possibly business rates purposes. We're honest that this is a bigger step than a family annexe and needs proper advice.
- How does drainage work for an annexe bathroom?
- We survey the levels on your plot to see whether the annexe can gravity-connect to the existing foul drainage. Where it can't, we design in a pumped or macerator connection, which is a common and reliable solution but does add cost.
- Will I have to pay separate council tax?
- A self-contained annexe can be given its own council tax band, though a discount or exemption often applies when it's occupied by a dependent relative. This is decided by your local authority, and we'd recommend checking with them directly once plans are drawn.
- How long does an annexe take from planning to completion?
- Planning permission typically takes eight to thirteen weeks to determine, followed by four to six weeks on site depending on size and the drainage work involved.
What our clients say
Reviews from homeowners across Sussex, Surrey and Kent.
"Best in class. None of my specific requests were any trouble at all. The team were polite, professional, smart, and accommodating throughout. A perfect example of how professional tradespeople should be."
"Alistair understood exactly how we wanted to use the garden. The finished space feels like a private retreat and we use it every day."
"Our garden office has completely transformed how we work from home. The quality is outstanding and the process was seamless."
Areas we cover
Designed and built by our own team across Sussex, Surrey and Kent.
West Sussex
East Sussex
Not on the list? See the full coverage map - we travel further for larger projects.
Read next
- Garden room planning permission guide
- How an insulated garden room is actually built
- Garden rooms with a shower and toilet
- The full garden room collection and build process
Considering an annexe?
We'll look at your plot, tell you honestly whether it needs full planning permission, and price the drainage and regs work properly from day one.