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The most common question families ask us before starting a project — and with good reason. Planning rules for granny annexes in the UK can seem complicated at first, but in most cases the answer is simpler than you’d expect.
The short answer: many of our annexes can be installed without full planning permission, either through permitted development rights or under the Caravan Act 1968. In most cases, The Green Room handles the entire planning process on your behalf — so you don’t need to become an expert.
This guide explains everything you need to know.
There are three main legal pathways for installing a granny annexe in England. Which one applies to your project depends on how your annexe is constructed, the size of your plot, and where you live.
Route 1 — The Caravan Act 1968 (most common for modular annexes)
Route 2 — Permitted development rights
Route 3 — Full planning permission
We’ll walk through each one clearly below.
If you’ve been researching granny annexes, you may have come across references to “the Caravan Act” and wondered what caravans have to do with a beautifully finished garden annexe. The answer is quite a lot — and it’s genuinely good news for you.
The Caravan Sites Act 1968 is a piece of UK legislation that contains a precise legal definition of what constitutes a “caravan” or “mobile home.” That definition is broader than most people expect. Under Section 13(2) of the Act, a structure qualifies as a caravan if it is designed for human habitation and is capable of being moved by road — even if it never actually moves during its entire lifetime.
This matters because structures that meet the legal definition of a caravan don’t require full planning permission, provided they are used as accommodation ancillary to a main dwelling — exactly how a granny annexe is used.
Because The Green Room’s annexes are built to Caravan Act specifications, our customers benefit from two significant advantages:
**No planning permission required** — in most cases, your annexe can be installed without a full planning application to your local council.
**Zero VAT** — structures that qualify under the Caravan Act are not subject to the standard 20% VAT that applies to traditional brick-built extensions. On a project worth £80,000–£130,000, that’s a saving of £16,000–£26,000.
To qualify under the Act, an annexe must meet specific construction criteria. The structure must:
– Be capable of being moved by road, either towed or transported on a vehicle or trailer
– Be constructed in no more than two sections, designed to be assembled on site using bolts, clamps, or similar fixings
– Not exceed the maximum size limits set out in the Act: no longer than 20 metres, no wider than 6.8 metres, and with internal ceiling height no greater than 3.05 metres
The Green Room’s annexes are designed and manufactured to meet all of these criteria. This doesn’t mean your annexe looks or feels like a mobile home — our builds are permanent. High-quality residential-grade homes indistinguishable from traditionally built structures. It simply means the construction method qualifies under the legal definition.
As well as the building meeting the construction criteria, the homeowner must also satisfy certain conditions:
– The annexe must be within the residential curtilage of your main property
– It must be occupied as accommodation ancillary to the main dwelling — typically by a family member
– It cannot be rented out as an independent property or given a separate postal address
– The property must be a house (not a flat or maisonette)
In straightforward terms: the annexe must be an extension of your household, not a separate home. This is exactly how the vast majority of our customers use their annexe.
We always recommend applying for a Lawful Development Certificate (LDC) from your local council, even when planning permission isn’t required. An LDC is a formal written confirmation from your council that your annexe is lawful. It protects you in the event of any future dispute — for example, when you come to sell your home. The Green Room manages this application on your behalf as part of our service.
Permitted development (PD) rights allow certain home improvements to be carried out without a full planning application. However, for granny annexes — which include a bedroom, kitchen, and bathroom — the rules are more restrictive than many people expect.
Under the Town and Country Planning (General Permitted Development) (England) Order 2015, an outbuilding can be built without planning permission as long as it is “incidental” to the main house. Government guidance specifically states that a building used as primary accommodation — with a bedroom, bathroom, and kitchen — goes beyond incidental use and generally falls outside permitted development rights.
This means that for most fully self-contained granny annexes, permitted development is not the appropriate route, and the Caravan Act is the better option. It is worth noting, however, that local authorities vary in their interpretation of these rules.
– The annexe must be located within the curtilage of a single house — not a flat or maisonette
– It cannot be positioned forward of the principal elevation of your home
– Maximum height of 4 metres with a dual-pitched roof (or 2.5 metres if within 2 metres of a boundary)
– The total area of outbuildings and extensions combined must not exceed 50% of the garden
– No verandas, balconies, or raised platforms above 0.3 metres
Properties in conservation areas, national parks, Areas of Outstanding Natural Beauty, or listed buildings have further restrictions. Permitted development rights may be removed or restricted for individual properties by an Article 4 Direction from the local authority.
If your project doesn’t qualify under the Caravan Act or permitted development, you will need to apply for full planning permission through a Householder Application to your Local Planning Authority. This is a formal application process, typically taking eight to twelve weeks.
The council will assess your proposal against local planning policies, considering factors including the size and appearance of the annexe, its relationship to neighbouring properties, and whether it is genuinely ancillary to the main dwelling.
Full planning applications are more common for:
– Properties in conservation areas or national parks
– Unusually large annexes
– Projects where the annexe is intended to be used by someone other than an immediate family member
– Properties subject to an Article 4 Direction
The Green Room has extensive experience managing planning applications across the UK. Where full permission is required, we work with specialist planning consultants to prepare and submit your application.
Regardless of which planning route applies, all our granny annexes comply with Building Regulations. This covers structural safety, insulation standards, fire safety, electrical installation, plumbing and drainage, ventilation, and energy efficiency.
Every Green Room annexe is designed and built to fully comply with current Building Regulations as standard.
A self-contained granny annexe may be subject to its own council tax banding. However, many local councils offer a discount — or even a full exemption — for annexes that are occupied by a dependent relative. The rules vary between councils, so we recommend checking with your local authority as part of your planning process.
The planning rules described in this guide apply to England. Permitted development rules in Scotland, Wales, and Northern Ireland differ in certain respects. If your property is outside England, please speak to our team and we can advise on the relevant rules for your location.
Planning can feel daunting, but you don’t have to navigate it alone. For every project we undertake, The Green Room will:
– Confirm which planning route applies to your property
– Manage the Lawful Development Certificate application on your behalf
– Handle full planning applications where required, working with specialist consultants
– Ensure your annexe is designed and built to comply with all Building Regulations
– Provide all documentation you need for your records
Our customers rarely need to deal directly with their council at all.
If you’re in Northamptonshire or the surrounding area, we’re here to help. Our team provides complete design, planning, and build services for granny annexes near you.
Book your free site survey or get in touch today to begin your project the easy way.
If a dependent relative lives in the garden annexe, you are usually exempt from council tax. Rules can vary slightly depending on your local council, but we can help guide you.
An LDC is formal confirmation from your local council that your annexe is lawful. It isn’t legally mandatory, but we strongly recommend obtaining one for your peace of mind and to protect your property’s future sale value. We manage this application on your behalf.
No. An annexe installed under the Caravan Act must remain ancillary to the main dwelling and cannot be rented out or given a separate postal address.
Yes, in most cases. Modular annexes built to Caravan Act specifications — including all of The Green Room’s annexes — typically do not require full planning permission, provided the homeowner conditions are met.
Conservation areas restrict permitted development rights, but the Caravan Act route is not affected by conservation area status. We will advise you on the specific rules for your property during your free consultation.
Still unsure which planning route applies to your property? Our team surveys hundreds of sites every year across the UK and can give you a clear, honest answer within minutes.
Book your free site survey today — we’ll handle the planning so you don’t have to.
If the local planning authority is satisfied that the appropriate legal tests have been met, it will grant a lawful development certificate. Read more on https://www.gov.uk/guidance/lawful-development-certificates
A Lawful Development Certificate (LDC) is a legal document stating the lawfulness of past, present or future building use, operations, or other matters. For technical information https://www.planningportal.co.uk/planning/planning-applications/consent-types/lawful-development-certificate
This article on The Home Owner Alliance website is an interesting read. The expense of later life care, increasing property prices, and the fact grown children are coming home (or never leaving), have all contributed to the rise in “granny” annexes in recent years.
Our team of down-to-earth experts genuinely care about great garden spaces and excellent customer service. Whether you’re just starting to explore your options or ready to move forward with your project, we’re here to help.