Granny annexe planning permission: do you need it?

The short answer: it depends on what the annexe is, where it goes and how it will be used. A granny annexe built as a permanent extension or outbuilding normally needs planning permission. But an annexe that legally counts as a caravan — which many modern timber and twin-unit annexes are designed to — can often be sited in your garden without a planning application, provided it stays part of your household.

“Often” is doing real work in that sentence. Whether your annexe falls on the right side of the line is a question of fact about your land, your household and the unit itself. The way to get that answer in writing, from your council, is a lawful development certificate.

The three routes for a granny annexe

Almost every garden annexe proposal ends up on one of three routes.

1. Planning permission. For a permanent building — an extension, or an annexe built on foundations as an outbuilding — or for anything that would amount to a separate home. The council weighs the merits: design, neighbours, policy.
2. Permitted development. Rights to build some outbuildings without an application. These cover buildings used incidentally to the house — a garden room, a gym, a store. They do not normally cover sleeping accommodation, so they are rarely the route for an annexe someone will live in.
3. A caravan used as part of the household. Siting a unit that meets the legal definition of a caravan, within the garden of your home, for use by your household. Done properly, this is not “development” needing permission at all — and a lawful development certificate confirms it.

The third route is the one most annexe manufacturers design for, and the one most often misunderstood.

When a granny annexe does not need planning permission

Planning permission is needed for “development”, which the law defines as building and other operations, or a material change in the use of land (Town and Country Planning Act 1990, s.55). Placing a caravan on land is not a building operation, and using one within the garden of your home as part of the same household is not, by itself, a change in how that land is used. For that position to hold, three things generally all have to be true:

• The unit is legally a caravan. It meets the statutory definition, including — for a twin-unit annexe — the limit of two sections and the maximum size. See the Caravan Act and garden annexes.
• It sits within the curtilage of your house. That means land genuinely forming part of your home’s garden — not a paddock or field you happen to own. See residential curtilage.
• Its use is ancillary to the house. The person living in it is part of your household, not a separate one. See ancillary occupation.

When it does need planning permission

The caravan route is not available, or not on its own, where:

• It would be a separate home. If it will be let, sold, given its own address, or lived in by a separate household, that is a new dwelling, and a new dwelling needs permission.
• It is not legally a caravan. Too large, more than two sections, or fixed in a way that means it can no longer be moved as a whole — at that point it is a building.
• The land is not garden. A paddock, orchard or field held with the house is often outside the curtilage, even when it is inside your title.
• The works around it are development. Concrete bases, retaining walls, new driveways or extensive landscaping can need permission in their own right, even where siting the unit does not.

Where a property is listed, or in a conservation area or National Park, the same tests apply, but the works around a unit can be more restricted and councils tend to look harder. It is worth getting advice before ordering.

Kitchens, bathrooms and “independent living”

A common worry is that giving an annexe its own kitchen and shower automatically makes it a separate dwelling. It does not, by itself. What matters is how the household actually functions — shared life, shared arrangements, one household rather than two. A fully equipped annexe lived in by a parent who is part of your family can be ancillary; a basic one let to a stranger is not.

Getting the answer in writing

Nothing obliges you to tell the council before siting a caravan-type annexe. The reason to apply for a lawful development certificate anyway is certainty. A certificate under section 192 of the 1990 Act is the council’s formal confirmation that what you have described would be lawful — something you can rely on if a neighbour complains, and hand to a buyer’s solicitor when you sell.

The council must normally decide within eight weeks of receiving the application (Development Management Procedure Order 2015, art. 39). Read more in our guides to lawful development certificates, what they cost and what happens if one is refused.

Before you order an annexe

Check these before you sign anything with a manufacturer:

1. Where exactly will it go — and has that land always been used as garden?
2. Who will live in it, and how will your household share life with them?
3. Can the manufacturer evidence that the assembled unit meets the caravan definition, including that it can be moved as a whole?
4. What base, services and access works will it need?
5. Is the property listed, or in a conservation area or National Park?

If any answer is uncertain, find out first. Our free eligibility check asks exactly these questions, and a person replies with an honest view.

Common questions

Can my mum or dad live in a granny annexe in my garden?

Yes, that is precisely the arrangement the caravan route suits — provided they live as part of your household and the annexe meets the other tests above.

Do I need planning permission for a granny flat?

“Granny flat” usually means accommodation converted within or attached to the house, which is assessed differently. A self-contained flat used as a separate home generally needs permission; accommodation used as part of the main home may not. The answer turns on the same question of use.

Is a lawful development certificate compulsory?

No. It is optional, but it turns “we believe this is lawful” into a formal determination from the council — which is worth a great deal when you sell, remortgage or face a complaint.

Sources

• Town and Country Planning Act 1990, section 55 (meaning of development)
• Town and Country Planning Act 1990, section 192 (certificates of lawfulness of proposed use)
• Caravan Sites and Control of Development Act 1960, section 29 (definition of caravan)
• Caravan Sites Act 1968, section 13 (twin-unit caravans)
• Town and Country Planning (Development Management Procedure) (England) Order 2015, article 39

Checked against the legislation in October 2026. This guide explains general principles for England; it is not advice on any particular property.