Planning permission is one of the first questions every family asks when considering a granny annexe, and it is often the one that causes the most confusion. The short answer is: it depends. Some granny annexes require full planning permission, while others can be built under permitted development rights or the Caravan Act without a traditional planning application at all. Understanding which route applies to your situation can save you months of delays, thousands of pounds in unnecessary fees, and a great deal of stress. In this guide, we will explain every planning route available for granny annexe planning permission in the UK, detail the specific rules and limits for each, and show you how Grannexe handles the entire process so you can focus on what matters: creating a comfortable home for your family member.
The Three Routes to Building a Granny Annexe
In England, there are three main routes for getting a granny annexe into your garden, each with different requirements, timescales, and implications. The route that applies to you depends on the size of the proposed annexe, the characteristics of your property, and your local planning authority's policies. Understanding all three options before you start will help you choose the most efficient and cost-effective path. The three routes are Permitted Development, the Caravan Act, and Full Planning Permission. Most families find that one of the first two routes applies to their situation, which means no traditional planning application is needed. Grannexe assesses which route is best for your property during our free site survey and handles all the paperwork regardless of the route.
- Permitted Development: build without a formal planning application if criteria are met
- Caravan Act: place a qualifying structure with a Certificate of Lawful Development
- Full Planning Permission: required when the other two routes do not apply
- Grannexe assesses the best route for your property during a free site survey
Permitted Development Rights: Building Without Planning Permission
Permitted development rights allow homeowners to carry out certain types of building work without submitting a formal planning application. For garden outbuildings, which include granny annexes, permitted development is available provided the structure meets a set of specific criteria. These criteria relate to size, height, position, and use. If your annexe falls within all of these limits, you have an automatic right to build it. However, permitted development is not available in all situations. If your home is a listed building, if you live in a conservation area, or if your permitted development rights have been removed by a previous planning condition (known as an Article 4 Direction), you will need to take a different route. It is also worth noting that permitted development covers the structure itself, but the annexe must remain ancillary to the main dwelling. This means it must be used by a family member or in connection with the main house, not as a completely separate household or rental property.
- The annexe must be single storey with a maximum eaves height of 2.5 metres
- Maximum overall height of 4 metres for a dual-pitched roof, or 3 metres for any other roof type
- The annexe must not be built forward of the principal elevation of the original house
- Total area of all outbuildings must not exceed 50% of the total curtilage (garden area excluding the original house footprint)
- No verandas, balconies, or raised platforms above 300mm
- If within 2 metres of a boundary, the maximum eaves height is 2.5 metres
- The annexe must be used for purposes ancillary to the main dwelling
The Caravan Act Route: Zero VAT and Simplified Planning
The Caravan Act 1960, as amended by the Caravan Sites Act 1968, provides an alternative and often more advantageous route for granny annexes. Under this legislation, a structure that meets the legal definition of a caravan can be stationed in a residential garden without full planning permission. Instead, you apply for a Certificate of Lawful Development (also called a Lawful Development Certificate or LDC), which is a simpler and faster process than a full planning application. The critical advantage of the Caravan Act route is VAT. Structures classified as caravans are zero-rated for VAT purposes, which means you pay no VAT on the build. On an annexe costing 110,000 pounds, that represents a saving of 22,000 pounds compared to a structure that attracts the standard 20% rate. This is completely legal, HMRC-compliant, and has been used by thousands of families across the UK. To qualify as a caravan under the Act, the structure must be capable of being moved (either in one piece or in no more than two sections), must not exceed certain dimensions, and must be designed for human habitation. Grannexe annexes are specifically engineered to meet these criteria. They are built as modular units in our factory, transported to site in sections, and assembled on a prepared base. This manufacturing approach is what makes the zero-VAT classification possible.
- A Certificate of Lawful Development (LDC) replaces full planning permission
- The LDC process is faster and simpler than a full planning application
- Zero VAT applies to structures classified as caravans, saving up to 20% of the build cost
- The structure must be transportable in one piece or a maximum of two sections
- Maximum dimensions apply: 20 metres long, 6.8 metres wide, and 3.05 metres internal height
- Grannexe annexes are specifically designed and built to meet Caravan Act criteria
- This route is fully legal and HMRC-compliant
Full Planning Permission: When You Need It
Full planning permission is required when your proposed annexe falls outside the limits of both permitted development and the Caravan Act. This is the most formal of the three routes and involves submitting a detailed application to your local planning authority, which then assesses the proposal against local and national planning policies. The decision typically takes 8 to 12 weeks. Common scenarios where full planning permission is needed include properties in conservation areas where permitted development rights are restricted, properties on Green Belt land, listed buildings or properties within the curtilage of a listed building, situations where the proposed annexe exceeds permitted development size limits, and properties where an Article 4 Direction has removed permitted development rights. While full planning permission takes longer and involves more paperwork, it is by no means a barrier. Thousands of granny annexes are approved through full planning every year. The key is to submit a well-prepared application that anticipates and addresses potential concerns. At Grannexe, we work with experienced planning consultants and architects to prepare applications that have the best possible chance of approval. We handle all drawings, supporting statements, and liaison with the planning authority on your behalf.
- Required for conservation areas, Green Belt, listed buildings, and Article 4 properties
- Also required when the annexe exceeds permitted development size limits
- Application is assessed against local and national planning policies
- Typical decision timeframe: 8 to 12 weeks
- Grannexe prepares and manages the entire application process
- Experienced planning consultants ensure the strongest possible submission
Conservation Areas and Green Belt: Special Rules
If your property is in a conservation area, permitted development rights for outbuildings are more restricted. Specifically, you cannot build any outbuilding to the side of your house under permitted development, and the total area of all outbuildings cannot exceed 50% of the garden. Additionally, some conservation areas have Article 4 Directions that remove permitted development rights entirely, meaning you must apply for full planning permission even for small structures. Green Belt presents a different challenge. National planning policy presumes against inappropriate development in the Green Belt. However, a granny annexe that is genuinely ancillary to the main dwelling, is proportionate in size, and does not have a greater impact on the openness of the Green Belt than the existing development can be acceptable. The planning authority will look carefully at the scale, design, and purpose of the annexe. Sensitively designed annexes that complement the existing property and landscape are more likely to be approved. Grannexe has experience building in both conservation areas and Green Belt locations. We understand the additional sensitivities and design our annexes accordingly, using appropriate materials, colours, and scales to satisfy conservation and Green Belt policies.
- Conservation areas: no outbuildings to the side of the house under permitted development
- Article 4 Directions can remove permitted development rights entirely
- Green Belt: national policy presumes against inappropriate development
- Ancillary, proportionate annexes can still be approved on Green Belt land
- Design, materials, and scale are critical in sensitive locations
- Grannexe has experience building in conservation areas and Green Belt
The Ancillary Use Requirement: What It Means in Practice
Regardless of which planning route you take, a granny annexe must be ancillary to the main dwelling. This means it must be used in connection with the main house and not as a completely independent, separate household. In practice, this typically means the annexe is occupied by a family member, a dependent relative, or someone with a close connection to the household in the main house. The annexe and the main house should share the same postal address and council tax account, and the annexe occupant should have some degree of shared use of the main house (even if this is occasional). The ancillary use requirement exists to prevent the creation of new, independent dwellings in gardens without proper planning scrutiny. If a planning authority determines that an annexe is being used as a separate dwelling rather than an ancillary space, they can take enforcement action. This is why it is important that the annexe is designed as a genuinely connected, dependent living space. Grannexe annexes are specifically designed with ancillary use in mind. They are comfortable, self-contained homes that provide independence and dignity, while remaining legally and practically connected to the main dwelling.
- The annexe must be used in connection with, not independently from, the main house
- Occupants are typically family members or dependent relatives
- The annexe and main house should share the same postal address and council tax
- Using an annexe as a completely separate rental property breaches ancillary use rules
- Enforcement action can follow if the ancillary requirement is not met
- Grannexe designs annexes that comply fully with ancillary use requirements
Common Reasons for Planning Refusal and How to Avoid Them
When a granny annexe planning application is refused, the reasons usually fall into a few predictable categories. Understanding these in advance allows you to design your annexe and prepare your application to avoid them. Overdevelopment is the most frequent reason for refusal. This occurs when the annexe, combined with other outbuildings, covers too large a proportion of the garden, or when the annexe itself is disproportionately large relative to the main house. Keeping the annexe modest in scale and ensuring adequate garden space remains is the best way to address this. Impact on neighbours is another common concern. Overlooking (windows facing a neighbour's private areas), loss of light, and overbearing bulk are the specific issues planning officers look for. Thoughtful positioning, appropriate window placement, and height controls address these concerns. Design quality matters too. An annexe that looks like an industrial container or clashes with the character of the area is more likely to be refused than one that complements the existing property and streetscape. Grannexe designs are carefully considered to blend with their surroundings. Finally, inadequate justification of need can lead to refusal. If the planning authority is not satisfied that the annexe is genuinely needed for ancillary residential use, they may refuse the application. A clear, honest supporting statement that explains who will live in the annexe and why is essential.
- Overdevelopment: keep the annexe proportionate and maintain adequate garden space
- Neighbour impact: position windows carefully and control height at boundaries
- Design quality: choose materials and finishes that complement the existing property
- Inadequate justification: provide a clear supporting statement about who will use the annexe and why
- Grannexe prepares supporting statements and designs to minimise refusal risk
- Pre-application advice from the local authority can identify issues before you submit
How Grannexe Handles Planning for You
Navigating granny annexe planning permission can feel overwhelming, which is why Grannexe manages the entire process from start to finish. When you contact us, the first step is a free, no-obligation site survey. During this visit, we assess your property, measure the available space, and identify which planning route is most appropriate. If your annexe qualifies for the Caravan Act route (as most of ours do), we prepare and submit the Certificate of Lawful Development application on your behalf. If permitted development applies, we can obtain a Lawful Development Certificate to give you written confirmation from the council that no planning permission is needed. If full planning permission is required, we work with our network of planning consultants and architects to prepare a comprehensive application, including detailed drawings, a design and access statement, and any supporting documents the planning authority requires. Throughout the process, we keep you informed at every stage. We liaise directly with the planning authority, respond to any queries or requests for additional information, and work to resolve any issues that arise. Our goal is to make the planning process as smooth and stress-free as possible, so you can focus on the exciting part: designing your annexe. With over 20 years of experience across Kent, London, and the South East, we have a strong track record of successful planning outcomes.
- Free site survey to assess your property and identify the best planning route
- Caravan Act applications (LDC) prepared and submitted on your behalf
- Permitted development certificates obtained for written council confirmation
- Full planning applications prepared with planning consultants and architects
- All drawings, statements, and supporting documents included
- Direct liaison with the planning authority throughout the process
- Over 20 years of successful planning outcomes across Kent, London, and the South East
Timescales: How Long Does the Planning Process Take?
The timescale for planning depends entirely on which route applies to your project. A Certificate of Lawful Development under the Caravan Act typically takes 6 to 8 weeks for the local authority to process, although some councils are faster. This is a determination of existing rights rather than a discretionary decision, so it is generally more predictable than full planning. Permitted development does not require any formal application, so there is no waiting period. However, we recommend obtaining a Lawful Development Certificate (which takes 6 to 8 weeks) to provide written proof that no planning permission is needed. This protects you in the future, for example if you sell the property. Full planning permission typically takes 8 to 12 weeks from submission to decision, assuming no complications. If the planning officer requests amendments or additional information, this can extend the timeline. Pre-application advice (an informal discussion with the planning authority before you submit) can add 4 to 6 weeks but significantly reduces the risk of delays later. At Grannexe, we begin the design and preparation process in parallel with planning, so that construction can start as soon as approval is confirmed. This approach minimises the overall timeline from first contact to a finished, habitable annexe.
- Caravan Act (LDC): typically 6 to 8 weeks
- Permitted development (LDC for confirmation): 6 to 8 weeks
- Full planning permission: 8 to 12 weeks (longer if amendments are needed)
- Pre-application advice: 4 to 6 weeks but reduces later delays
- Grannexe runs design and preparation in parallel with planning to save time
Conclusion
The question of whether you need granny annexe planning permission does not have a one-size-fits-all answer, but the good news is that the vast majority of projects have a workable route. Permitted development, the Caravan Act, and full planning permission each offer a path to getting your annexe built, and Grannexe has deep experience with all three. The Caravan Act route is particularly attractive because it combines simplified planning with zero VAT, saving you thousands of pounds on a build that starts from just 90,000 pounds. Whatever your situation, we handle the planning process from start to finish, drawing on over 20 years of experience building granny annexes across Kent, London, and the South East. The best first step is to book a free, no-obligation site survey. We will assess your property, identify the right planning route, and give you a clear, honest picture of what is involved.
Frequently Asked Questions
Do I need planning permission for a granny annexe in my back garden?
In many cases, no. If your annexe meets the criteria for permitted development or qualifies under the Caravan Act, you do not need full planning permission. The Caravan Act route, which Grannexe specialises in, requires a Certificate of Lawful Development rather than a traditional planning application. Full planning permission is only needed for larger annexes or properties in restricted areas such as conservation areas or Green Belt.
What is the Caravan Act and how does it apply to granny annexes?
The Caravan Act 1960 defines a caravan as a structure designed for human habitation that can be transported in one piece or a maximum of two sections. Modular granny annexes that meet this definition can be placed in a residential garden with a Certificate of Lawful Development instead of full planning permission. Critically, structures classified as caravans are zero-rated for VAT, saving you up to 20% of the build cost. Grannexe annexes are specifically designed to qualify.
Can I build a granny annexe in a conservation area?
Yes, but the rules are stricter. Permitted development rights are more limited in conservation areas, and some have Article 4 Directions that remove these rights entirely. In most cases, you will need full planning permission, which means the design, materials, and scale of the annexe must be sensitive to the character of the area. Grannexe has experience building in conservation areas and designs annexes that satisfy conservation policies.
How long does it take to get planning permission for a granny annexe?
A Certificate of Lawful Development under the Caravan Act typically takes 6 to 8 weeks. Full planning permission takes 8 to 12 weeks from submission. Pre-application advice can add 4 to 6 weeks but often speeds up the formal process. Grannexe begins design and preparation in parallel with the planning process to minimise the overall timeline.
What are the most common reasons for granny annexe planning refusal?
The most common reasons are overdevelopment (the annexe is too large relative to the garden or main house), impact on neighbours (overlooking, loss of light, or overbearing bulk), poor design quality, and inadequate justification of the need for the annexe. All of these can be addressed with careful design and a well-prepared application, which is exactly what Grannexe provides.
Does Grannexe handle the planning application for me?
Yes. Grannexe manages the entire planning process, whichever route applies. This includes site assessment, preparation of all drawings and documents, submission of the application or certificate, liaison with the planning authority, and resolution of any issues that arise. Planning management is included as part of our service at no additional charge.