Granny annexe without planning permission: how the Caravan Act route works
A granny annexe can be sited in a garden without a planning application if it meets the legal definition of a twin-unit caravan under the Caravan Acts of 1960 and 1968 and is used as part of the main household. Most are made to BS3632, the residential park home standard. It is not a way round the rules; it is a different set of rules, with a certificate at the end of it.
This page explains how the route is generally understood to work, so that readers know what to ask. The position for any particular site and building is for the supplier, the local planning authority and, on VAT, an accountant to confirm.
In short
- The rules: a self-contained annexe is never covered by Permitted Development, so it needs either planning permission or to qualify as a caravan. The Caravan Act is the second of those.
- The route: there is no planning application. The annexe is built as a twin-unit caravan, usually to BS3632, sited for use ancillary to the house, and usually confirmed by a Lawful Development Certificate.
- The building: no more than two sections, joined on site; once assembled it must still be capable of being moved by road; and it must fit within 20m long, 6.8m wide and 3.05m internal height.
- VAT: a BS3632 annexe supplied this way may be zero-rated. On a £90,000 building that is up to £18,000, so the treatment should be confirmed in writing.
- Your site: none of this is fixed for every site. Confirm the position for yours with the supplier and the local planning authority, and take advice from a tax accountant on the VAT.
Can you build a granny annexe without planning permission?
Yes, but not in the way the phrase suggests. There is a route with no planning application, but it has rules of its own, and most people confirm it with a Lawful Development Certificate.
No annexe with its own kitchen, bathroom and sleeping space can be built under Permitted Development, the rights that let most garden rooms go up without an application. A building designed for someone to live in is outside those rights entirely, so “no planning permission” never means “no rules”.
What the Caravan Act route offers instead is a way to site the annexe without a planning application. If the annexe meets the legal definition of a caravan and is used in connection with the main house, siting it is not treated as development that needs planning permission. The homeowner can then apply to the local planning authority for a Lawful Development Certificate, which confirms that position in writing. It isn’t compulsory, but it is strongly advisable. That is the route many dedicated annexe specialists now supply their buildings under, and it is the one this page explains.
The other route is a full planning application with Building Regulations sign-off. Both are legitimate. The comparison further down sets out where each makes sense.
What is the Caravan Act route for a granny annexe?
The Caravan Act route rests on the definition of a caravan in the Caravan Sites and Control of Development Act 1960, extended to twin units by the Caravan Sites Act 1968, which covers twin units: a structure built in no more than two sections, designed to be assembled on site with bolts, clamps or other devices, and physically capable of being moved by road once assembled. The 1960 Act’s own definition is a structure designed or adapted for people to live in that can be moved from one place to another. A building that meets that definition is treated in law as a caravan. A pitched roof, insulated walls, a fitted kitchen and a bathroom don’t stop it being a caravan, even if it looks and works like a permanent building. But one that is too large, too permanent or fixed to the ground may be treated as a building instead.
That classification is what changes the planning position. Stationing a caravan within the curtilage of a house (the garden and grounds that go with it), for use ancillary to that house, does not need planning permission in the way a new building does. The annexe is usually made off-site, often to BS3632, delivered in up to two sections, joined together on a prepared base, and connected to services. In practice it is never moved again. The law only requires that it could be.
Full Planning Permission with Building Regulations
- Consent
- A planning application to the local authority, then Building Regulations sign-off by building control.
- Status
- A permanent building with planning permission.
The Caravan Act with a Lawful Development Certificate
- Consent
- No planning application. A Lawful Development Certificate confirms the siting is lawful.
- Status
- A residential mobile home, usually built to BS3632.
What does BS3632 mean for the building?
BS3632 is the British Standard for residential park homes: the specification for a twin-unit caravan built for year-round living. The current edition is BS 3632:2023. It sets requirements for thermal insulation, structural strength, ventilation, and the electrical and plumbing installations, at a level intended for year-round living rather than holiday use. A company supplying an annexe under the Caravan Act should be able to show that the building is manufactured and certified to it.
For the buyer, BS3632 does two jobs. It is the main published benchmark for year-round living, in place of Building Regulations, which are generally understood not to apply to a structure classified as a caravan. And it is one of the conditions HMRC sets for zero-rating, covered below. The Caravan Acts themselves don’t mention BS3632, so it isn’t what makes the annexe lawful. But an annexe on this route that isn’t built to it loses the VAT zero rate and the main published benchmark for year-round living.
The standard governs the fabric and the services, not the appearance. Cladding, roofline, glazing and internal finish are the supplier’s design decisions, which is why Caravan Act annexes from different suppliers look nothing like one another and nothing like a park home.
The two-section rule and the size limits
The twin-unit definition is the part of the law that shapes the building most. The annexe can be made in no more than two sections, joined on site, and once assembled it must still be physically capable of being moved by road. The junction between the two halves is engineered into the structure from the outset; inside, it is closed and finished, and there is nothing to see. Timber frame, SIPs and interlocking timber systems can all be detailed this way. It is a design constraint on the structure, not a limit on how solid or permanent the finished building feels.
The Act also sets maximum dimensions for a twin-unit caravan:
| Dimension | Maximum | Measured |
|---|---|---|
| Length | 20 metres | Excluding any drawbar |
| Width | 6.8 metres | Overall |
| Height of living accommodation | 3.05 metres | Internally, from the floor at the lowest level to the ceiling at the highest level |
Source: Caravan Sites Act 1968, section 13, as amended.
Almost every standard annexe design sits comfortably inside these figures. A 20m × 6.8m footprint is 136sqm, which is larger than most two-bedroom annexes. The one to watch is height: 3.05m is an internal measurement, so a vaulted ceiling under a dual-pitched roof has to be designed with it in mind. Any company working on this route will know the limits; the question to ask is simply whether the design you are being shown has been checked against them.
What is a Lawful Development Certificate, and why apply for one?
A Lawful Development Certificate is a formal decision from the local planning authority that a particular use or development is lawful and does not need planning permission. On the Caravan Act route it is the document that establishes the annexe’s position. It is not planning permission, and it does not grant anything; it confirms that, on the facts submitted, the siting of the annexe as a caravan for ancillary use is lawful.
It is possible to site a Caravan Act annexe without one. Few people who understand the route would choose to. Without a certificate, the lawfulness of the annexe rests on the homeowner’s own reading of the law, which is a poor position to be in if a neighbour objects, the council queries it, or the house is sold. A buyer’s solicitor may ask for it. Many annexe specialists apply for the certificate as part of their service, and some work with annexe planning consultants who prepare the application. Either way, the certificate should be in hand before the building is ordered, not after it arrives.
Read more: Lawful Development Certificates for garden rooms and annexes → · Annexe planning consultants →
Can a Caravan Act annexe be zero-rated for VAT?
The difference between zero-rated and 20% VAT on the building itself.
The VAT position
HMRC’s rule, set out in VAT Notice 701/20, is that a caravan is zero-rated if it is over 7m long or 2.55m wide and is manufactured to BS3632. Most Caravan Act annexes are designed to meet both tests. Zero-rated means no VAT is charged on the supply of the building, which on a £90,000 annexe is a difference of up to £18,000 against the same building bought on the full planning route at 20%.
Annexe by Future Rooms shows the difference more clearly than most, because it publishes the price of each model on both routes. Its Hanley one-bedroom is £98,840 built to BS3632, with VAT at 0%, and £124,608 built to Part L of the Building Regulations: £103,840 for the building plus £20,768 VAT.
Two qualifications matter, and there may be others depending on the building and the supplier. The zero rate applies to the building, not to removable contents: furniture, free-standing appliances and similar items are standard-rated even when the supplier provides them. And the building has to be genuine living accommodation, with washing facilities and a means of preparing food; check the specification with the supplier.
This is the single biggest reason two annexe quotes at the same headline price can be very different in what they buy. A price quoted zero-rated on the Caravan Act route and a price quoted including 20% VAT on the planning route are not comparable. Before signing, the supplier should confirm in writing that the building qualifies for zero-rating under their supply route.
Take advice on the VAT
The Guide is not a tax adviser, and the VAT position depends on the building, the supplier and how the sale is structured. Where the saving is material to the budget, which for most buyers it will be, ask a tax accountant to review the supplier’s written confirmation before committing. HMRC’s own guidance is VAT Notice 701/20.
Read more: How much does a granny annexe cost? →
What does ancillary use mean in practice?
The Caravan Act route depends on the annexe being used in connection with the main house, which planning officers call ancillary use. That is the basis on which the Lawful Development Certificate is granted, and it has to keep holding after the building is occupied.
Councils look at the facts as a whole. The signs include an occupant who is family or closely connected to the household, a garden and day-to-day life shared with the house, no separate postal address, and no separate sale or letting. Services usually run from the main house rather than through separate meters. No single point settles it either way.
- Letting it to a tenant, or as a holiday let through a site such as Airbnb. These are different uses, but either may be a change of use or break a condition, so raise it with the council first.
- Separate access that isolates the annexe from the house, or changes that would let it be sold on its own.
- Running a business from it that has nothing to do with the household.
Having friends or family to stay is exactly what ancillary use allows. Letting income is a different matter, and if it is part of the plan it should be raised before the certificate is applied for. If the use changes, the council can look at the position again, and may ask for a planning application or take enforcement action.
For a relative with a disability or care need
A Lawful Development Certificate is decided on the facts, not on merit, so a care need doesn’t count in its favour as such. But a care arrangement can help show that the annexe is used as part of the home, so describe the intended occupant and their needs clearly.
Caravan Act or full planning permission?
The two routes are compared side by side in the garden annexe guide. In short: full planning permission usually takes longer, usually carries 20% VAT and gives you a permanent building with planning permission; the Caravan Act route is often faster, may be zero-rated, and leaves the annexe classified as a residential mobile home.
That last point is the one to weigh. A Caravan Act annexe has no planning permission behind it, only, if you apply for one, a certificate that its siting is lawful. The route is widely used and well understood by conveyancers, and in practice the building is never moved, but some purchasers and mortgage lenders are more comfortable with a full planning history. Anyone likely to sell in the medium term should raise it with their estate agent.
Some builders choose not to use the route at all. Swift Unlimited, who build with full planning permission, set out their reasons in a guest post: Planning permission or the Caravan Act? A builder’s view of the risks.
The dual route
Some specialists submit a full planning application and a Caravan Act application at the same time, so that if one runs into difficulty the other may succeed. It adds cost and a little time. For a site with any uncertainty, a conservation area, say, or a difficult neighbour, it is worth asking whether they would recommend it.
How to find a company that builds Caravan Act annexes
The Caravan Act route is a specialism. It needs a building engineered for the two-section rule, manufacturing certified to BS3632, and a Lawful Development Certificate application prepared properly. Companies that build garden rooms and occasionally add a kitchenette do not, as a rule, offer any of those things, however the building is described. The ones that do will say so plainly and will have done it many times.
Four questions sort them quickly. Most annexe specialists run installation teams that cover a wide area, so the field is not limited to whoever is based nearest.
- Is the building certified to BS3632?
- Who prepares the Lawful Development Certificate application?
- Will the VAT treatment be confirmed in writing?
- Can you show a completed annexe on this route that I can visit?
Find Caravan Act annexe specialists that cover your area
The Garden Room & Annexe Directory lists UK companies that build annexes under the Caravan Act, filtered to your location.
Official guidance
This page explains the rules in plain English. The official wording is in these sources, and where a council takes a different view of a particular case, the council decides, subject to appeal. An experienced annexe designer will walk you through the routes at the design stage, and planning consultants can advise where a site is less straightforward. But as the householder, it’s your responsibility to confirm your own position.
- Caravan Sites and Control of Development Act 1960, section 29
- The legal definition of a caravan, on legislation.gov.uk.
- Caravan Sites Act 1968, section 13
- Twin-unit caravans: no more than two sections, movable by road once assembled, and the 20m × 6.8m × 3.05m limits.
- Caravans Act (Northern Ireland) 2011, section 15
- The same twin-unit definition and limits in Northern Ireland.
- Lawful development certificates (GOV.UK guidance)
- What a certificate confirms, how to apply and how long the council has to decide.
- Planning fees in England (GOV.UK)
- The current fee schedule for planning applications and certificates.
- Building Regulations 2010, Schedule 2
- The exemptions for small buildings, which don’t apply where there’s sleeping accommodation.
- HMRC VAT Notice 701/20: caravans and houseboats
- When a caravan annexe can be zero-rated: the size test and BS 3632.
Frequently asked questions
- Do you need planning permission for a granny annexe?
- A granny annexe can’t be built as an ordinary garden building, because Permitted Development does not cover a building someone will live in. There are two routes: a full planning application with Building Regulations, or the Caravan Act route, where the annexe is built to BS3632 as a twin-unit caravan and its siting is confirmed by a Lawful Development Certificate.
- Can you build a granny annexe without planning permission?
- Yes, under the Caravan Act route. The annexe meets the legal definition of a twin-unit caravan (no more than two sections, joined on site, and movable by road once assembled) and is sited within the curtilage of the house and used as part of the main home, not as a separate one. Siting it does not need a planning application; a Lawful Development Certificate confirms that in writing. The certificate is optional, but strongly advisable.
- What is the Caravan Act?
- The Caravan Acts of 1960 and 1968 define a caravan; the 1968 Act covers twin units built in no more than two sections, assembled on site, and capable of being moved by road once assembled, within 20m long, 6.8m wide and 3.05m internal height. A granny annexe built to that definition is legally a caravan, which is why it can be sited in a garden without a planning application.
- Is a Caravan Act annexe VAT free?
- It may be zero-rated. HMRC zero-rates a caravan over 7m long or 2.55m wide that is manufactured to BS3632, which most Caravan Act annexes are. The zero rate covers the building, not removable contents such as furniture. Ask the supplier to confirm the treatment in writing, and have a tax accountant review it before committing.
- Does a Caravan Act annexe pay council tax?
- Usually an annexe is assessed for council tax in its own right, whichever route it was consented under. In England and Wales an annexe occupied by a dependent relative may be exempt, and in England a 50% reduction applies where the annexe is a relative’s main home, or is used by someone in the main house as part of their own home. The rules depend on circumstances and differ in Scotland and Wales, so confirm the position with the local council and the Valuation Office (part of HMRC) in England and Wales, or the Assessor in Scotland. Council tax on an annexe: where to check →
Last updated October 2026 · Part of our garden annexe guide.
