You've seen granny annexes and thought: could I have one in my garden? The first question is always the same: is my garden actually big enough, and will the council let me build one? The good news is that far more gardens are suitable than people initially realise, and planning success rates for well-designed annexes are encouragingly high. At Grannexe, based in Biggin Hill, Kent, we've assessed hundreds of gardens and built annexes in spaces that homeowners initially thought were too small, too awkward, or too challenging. In this comprehensive guide, we'll help you assess your garden's genuine potential, understand what planning authorities actually look for, identify common challenges and how to overcome them, and take practical first steps toward finding out for certain.
The Quick Answer
Can you build a granny annexe in your garden? In most cases, yes. If you have a reasonably sized garden (not just a small patio or yard), rear or side access wide enough for construction equipment to reach the site, no major prohibitive planning restrictions on your specific property, and a genuine family need for the accommodation, then you probably can build an annexe. But the details matter significantly, and that's what this comprehensive guide covers.
How Much Garden Space Do You Actually Need?
There's no official minimum garden size for an annexe, but here are practical guidelines based on our extensive experience:
- Studio annexe (open-plan design): Needs approximately 35-45 square metres of footprint
- One-bedroom annexe: Needs approximately 45-55 square metres of footprint
- Two-bedroom annexe: Needs approximately 55-70 square metres of footprint
- Plus: Access space around the annexe for maintenance and fire safety
- Plus: Adequate remaining garden space to avoid overdevelopment concerns
- Practical rule of thumb: If you could comfortably fit a double garage in your garden, you can probably fit an annexe
The 'Remaining Garden' Consideration
Planning authorities don't just assess whether the annexe physically fits. They consider whether adequate garden remains after building. This assessment is somewhat subjective, but general guidance suggests:
- The annexe shouldn't visually dominate the garden; it should feel subsidiary to the main house
- Some genuinely usable outdoor space should remain after the annexe is built
- The main house shouldn't feel cramped, enclosed, or overlooked by the annexe
- Corner plots and L-shaped gardens often work better than very narrow rectangular strips
- Smaller gardens can absolutely work if the annexe design is appropriately modest in scale
Access: Getting the Annexe Into Your Garden
This is frequently the make-or-break practical factor. Granny annexes are manufactured in sections and craned into position. You typically need:
- Vehicle access for delivery lorries: Typical width needed is approximately 3 metres minimum
- Crane access or clear lifting space above the garden
- A clear, negotiable path from the road to the final annexe position
- If access is via neighbours' land or shared driveways, their explicit permission is essential
- Difficult access isn't necessarily impossible but may add complexity and cost
What If I Don't Have Side Access?
Many properties only have access through the house itself or have no practical vehicle access at all. Options include:
- Crane over the house: If there's crane positioning space at the front, annexe sections can be lifted over the roof
- Smaller modular sections: Breaking the annexe into smaller, manageable components that can be hand-carried through the house
- Temporary fence removal: If neighbours agree, temporary access through their property during delivery
- Road crane: Larger cranes positioned on the public road (requires council permits but is often achievable)
- We carefully assess access during our free site visit and advise honestly on practical solutions
Understanding Your Property's Planning Situation
Before investing heavily in detailed plans, understand your property's specific planning context:
- Conservation Areas: Additional design scrutiny applies; permission is still achievable but designs need to be more sympathetic
- Listed Buildings: Additional Listed Building Consent may be required; usually possible but more complex
- Areas of Outstanding Natural Beauty (AONBs): Stricter policies apply; not impossible but more challenging
- National Parks: Similar to AONBs with stricter environmental scrutiny
- Article 4 Directions: Local restrictions removing permitted development rights; full planning permission required
- Tree Preservation Orders: Protected trees cannot simply be removed; you must design around them
- You can check your area's status on your local council's planning website or ask us during your consultation
The Size of the Annexe Relative to Your House
Planning officers assess whether the annexe is genuinely 'ancillary' (subsidiary) to the main house. This practically means:
- The annexe should be clearly smaller than the main house
- There's no fixed official ratio, but significant disparity helps your application
- A large annexe proposed next to a small house raises legitimate red flags
- Very large annexes may be assessed as separate dwellings rather than ancillary accommodation
- We advise on appropriate sizing relative to your specific house during our site assessment
Impact on Neighbouring Properties
Planning applications consider how your annexe would affect neighbouring properties:
- Overlooking: Annexe windows facing directly into neighbours' windows or private garden areas
- Overshadowing: The annexe potentially blocking natural light to neighbours' spaces
- Noise: Potential concerns about additional residents close to boundary lines
- Visual impact: The annexe appearing dominant or overbearing from neighbours' views
- Good, thoughtful design mitigates all these concerns; single-storey annexes typically cause few genuine issues
Ground Conditions and Garden Slopes
Your garden's existing terrain affects both feasibility and cost:
- Level gardens: Simplest and most economical for foundation preparation
- Sloping gardens: Achievable but may need raised platforms, stepped foundations, or cut-and-fill earthworks
- Poor drainage: Gardens with drainage problems need solutions to prevent waterlogging around the annexe
- Trees and root systems: May need protection measures or root barriers during construction
- Underground services: Existing drains, cables, and pipes may need careful routing or even relocation
Services: Connecting to Water, Electricity, and Drainage
Your annexe needs utility connections from the main house. Consider:
- Distance from main house to annexe position: Longer distances mean longer and more expensive trenches
- Electric capacity: Your existing supply must comfortably support additional annexe demand (usually fine)
- Water pressure: Very long distances may require pressure boosting
- Drainage: Connection to existing house drains or, for distant annexes, alternative treatment systems
- Connections within 10-15 metres are typically straightforward; beyond that distance adds progressively to cost
Common Obstacles and Practical Solutions
We've encountered most conceivable obstacles in our years of experience. Common issues and their solutions:
- Garden too narrow: Consider a narrower, more compact annexe design or different positioning
- No apparent side access: Crane over the house or use smaller modular construction sections
- Very close to boundary: Design carefully to minimise genuine impact on neighbours
- Significantly sloping site: Platform foundations, split-level designs, or stepped construction
- Trees obstructing the site: Design creatively around them or, if not protected, seek removal permission
- Previous planning refusal: Understand exactly why it was refused and address those specific concerns in a new application
The Free Site Assessment: Your Essential First Step
The only way to know for certain is a professional assessment by experienced specialists. At Grannexe, we offer completely free site visits where we:
- Accurately measure your garden and assess genuinely usable space
- Evaluate access routes and realistic delivery options
- Identify any planning constraints specifically affecting your property
- Discuss your requirements and recommend suitable annexe sizes and designs
- Advise honestly on likely planning success based on our extensive local knowledge
- Provide an initial cost estimate for realistic budgeting
- All with absolutely no obligation to proceed; just useful, honest information to help you decide
What Happens If We Identify Genuine Problems?
Sometimes our site assessments reveal significant challenges. If that happens, we will:
- Explain the issue clearly, honestly, and without sugar-coating
- Suggest potential creative solutions if any genuinely exist
- Advise if a smaller, different, or repositioned annexe might work instead
- Recommend pre-application discussions with your local council if that would help clarify the position
- Never push you toward a project that isn't genuinely feasible
- We'd always rather tell you honestly than accept money for a planning application that will inevitably fail
Conclusion
Most gardens can accommodate a granny annexe. The real question isn't usually 'can I?' but 'what's the best approach for my specific situation?' That's where professional assessment makes the crucial difference. At Grannexe, based in Biggin Hill, Kent, we've built annexes in gardens of all shapes, sizes, and apparent challenges across Kent and the South East. We know what works, what doesn't, and how to overcome common obstacles creatively. We're happy to visit your home, assess your garden thoroughly, and give you a completely honest appraisal of what's realistically possible. Call us on 01689 818400 to arrange a free site visit. There's no obligation whatsoever, just practical, expert advice to help you make a genuinely informed decision.
Frequently Asked Questions
What's the absolute minimum garden size for a granny annexe?
There's no fixed official minimum, but practically you need enough space for the annexe footprint (35-70 square metres depending on size chosen) plus access around it and some remaining usable garden space. Gardens of 100+ square metres usually have good workable options available.
My garden backs directly onto open fields. Does that make planning easier?
It can help significantly as there are no rear neighbours to consider or impact. However, if the adjacent fields are designated Green Belt or protected agricultural land, your property may have specific restrictions. We assess each unique situation individually.
Can I build a granny annexe in my front garden instead of the back?
Front garden annexes are theoretically possible but face considerably more planning scrutiny due to visual impact on the public street scene. Most annexes are built in rear gardens where they're less publicly visible and more obviously domestic.
What if my neighbour actively objects to me building an annexe?
Neighbour objections don't automatically prevent planning approval. Only 'material planning considerations' like genuine overlooking or measurable loss of light carry legal weight. We design thoughtfully to minimise any legitimate concerns wherever possible.
I have a long, narrow garden. Can I still have an annexe?
Yes. Narrow gardens can accommodate appropriately designed narrower annexes. Our studio designs are only about 6 metres wide. We design specifically to fit your available space and constraints.
Will the annexe completely block my view of the rest of the garden?
Good design and thoughtful positioning minimise this concern. Annexes are typically placed at the rear of the garden, preserving the garden view from the main house. We discuss optimal positioning carefully during every site assessment.
What happens if planning permission is refused despite our best efforts?
We achieve a 95%+ success rate, but refusals do occasionally happen. We can appeal to the Planning Inspectorate, modify the design and resubmit addressing the specific concerns, or sometimes pursue the Caravan Act route as an alternative. We don't give up easily on families who genuinely need an annexe.
Do I need to formally inform my neighbours before starting to build?
For formal planning applications, the council notifies neighbours as part of the statutory process. However, we strongly recommend speaking to neighbours personally and informally first. Most people are genuinely supportive when they understand it's for family care, not commercial exploitation.