What is an annexe? Meaning, types and how they work
An annexe is extra living accommodation that belongs to a main house, either attached to it or standing separately in the garden. A self-contained annexe has its own front door, kitchen, bathroom and somewhere to sleep, so someone can live in it independently while staying part of the same household and property.
Illustrated from a scale model by The Garden Room & Annexe Guide.
In short
- What it is: additional accommodation that belongs to a main house. Most people searching for one mean a self-contained annexe that someone can live in.
- The two kinds: attached to the house, built much like an extension, or detached in the garden, often called a garden annexe or granny annexe.
- What keeps it an annexe: it is used in connection with the main house. Letting it or selling it as a separate home is a different planning question.
- Spelling: in British English, annexe is the building and annex is the verb. Annex is also the American spelling of the building, and both appear on UK property listings.
What does “annexe” mean for a house?
In property terms, an annexe is a building, or part of a building, that adds accommodation to a main house and belongs to the same property.
The word covers a range of things, from a bedroom suite over a garage to a two-bedroom home at the bottom of the garden. What most people mean, and what this guide covers, is a self-contained annexe: one with its own entrance, kitchen, bathroom and sleeping space, so that the person living there does not need to use the main house day to day.
That independence is the point. It lets a parent, an adult child or a relative with care needs live close to the family without sharing a kitchen or giving up their own front door.
Granny annexe, granny flat, granny pod. These are informal names for the same thing, a self-contained annexe for a relative. “Granny flat” tends to mean accommodation inside or attached to the house. “Granny pod” usually means a compact, factory-built annexe in the garden.
Attached to the house, or in the garden
An annexe either joins the house or stands on its own in the garden. Most specialist companies build the second kind.
An attached annexe is built onto the house, or created from part of it, such as a converted garage or a wing with its own door. It is built and approved much like an extension.
A detached annexe stands on its own in the garden. It is usually called a garden annexe or granny annexe. It can be built with full planning permission and Building Regulations, or sited under the Caravan Act as a residential mobile home, built to BS3632, with a Lawful Development Certificate. Either way it is a home held to a residential standard, not a garden building with a bathroom added.
Some specialists build both. Bridge Garden Rooms build granny annexe extensions attached to the house as well as standalone annexes in the garden.
- Studio
- Ark Design Build’s 19.84sqm annexe in Esher fits a kitchenette and shower room beside one main room.
- One bedroom
- Executive Garden Rooms’ 9m × 5m annexe in Hampshire has an open-plan kitchen and living room, a bedroom and a shower room.
- Two bedrooms
- Timeless Garden Rooms’ 85sqm annexe has an en-suite for each bedroom.
Annexe or garden room?
From the outside the two can look alike. The difference is what they are for and the standard they are built to.
A garden room is for daytime use, such as an office, a gym or a hobby room, and is usually built under Permitted Development. An annexe is for living in, so it always needs formal consent and has to meet a residential standard: Building Regulations, or BS3632 on the Caravan Act route.
Adding a kitchenette and a shower to a garden room does not turn it into an annexe. Someone can only live in it legally once it has been built to that standard and approved for that use.
Annexe or separate home?
What keeps a building an annexe is how it is used.
The planning term is ancillary: the annexe is used in connection with the main house, by family, guests or someone who is part of the household, and it is not a separate home in its own right. Planning permissions for annexes usually say so in a condition. On the Caravan Act route, ancillary use is part of the legal basis for siting the building at all.
If the annexe is let to someone unconnected with the household, or sold off separately, it is likely to be treated as a new dwelling. That needs its own planning permission, which is often harder to get than permission for an annexe. If letting it, or using it for holidays, is part of the plan, raise it at the very start with the builder and the local planning authority.
Council tax, value and mortgages
Three questions that come up early, each with its own answer.
- Council tax
- A self-contained annexe can be given its own council tax band, but discounts and exemptions may reduce the bill or remove it altogether, depending on who lives there. The rules differ between England, Wales and Scotland. Council tax on a granny annexe: where to check.
- Does an annexe add value?
- For buyers who want space for a relative, an adult child or guests, a well-built annexe adds to a property’s appeal. How much value it adds depends on the area, the building and how it was approved. An annexe with full planning permission is on the property record as a permanent building. A Caravan Act annexe is classified as a mobile home, which is well understood but not something every buyer or lender is equally comfortable with.
- Mortgages
- Lenders vary in how they treat a house with an annexe. Some look closely at how it was approved and whether it could be let separately. If you are buying a house with an annexe, ask the seller for the planning permission or Lawful Development Certificate early, and tell your broker about the annexe at the outset.
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Frequently asked questions
- What does annexe mean in a house?
- An annexe is additional living accommodation that belongs to a main house, either attached to it or standing separately in the garden. A self-contained annexe has its own entrance, kitchen, bathroom and sleeping space, so someone can live in it independently while it remains part of the same property.
- Is it annex or annexe?
- In British English, annexe is the noun for the building and annex is the verb, as in to annex territory. Annex is also the American spelling of the noun. Both spellings are used on UK property listings and mean the same building.
- What is the difference between an annexe and an extension?
- An extension adds rooms to the main house and is used as part of it. An annexe is self-contained accommodation, with its own entrance, kitchen and bathroom, so someone can live in it independently. An annexe can be attached to the house or detached in the garden.
- Can I rent out my annexe?
- Not without checking first. Most annexes are approved for use in connection with the main house, by family, guests or a member of the household. Letting it to someone unconnected may count as creating a separate dwelling, which needs its own planning permission. Raise it with your local planning authority before you build or let.
- Do you pay council tax on an annexe?
- A self-contained annexe can be given its own council tax band, but there are discounts and exemptions that may reduce or remove the bill, depending on who lives there and where in the UK you are. Your local council makes the decision.
Find annexe specialists that cover your area
The Garden Room & Annexe Directory lists UK annexe specialists, filtered by location, planning route and design approach.
Last updated October 2026 · Part of our garden annexe guide.
