How to create a granny annexe that works for everyone

A granny annexe is self-contained accommodation within or attached to your main home, usually with its own bedroom, bathroom and kitchen.

You might also hear it called a granny flat, granny pod or garden annexe, but it is different to a garden room which is usually an extra space for working, exercising or relaxing rather than somewhere designed for independent living.

A granny annexe normally needs to remain ancillary to the main home rather than becoming a separate dwelling. And when it’s done well, it can give a family member somewhere that feels entirely their own whilst keeping you nearby.

There are lots of reasons that several generations might live under one roof – or at one address. For some families, a granny annexe means an ageing parent can stay close to the people they love while keeping their independence. For others, it gives grown-up children somewhere affordable to live while they save for a home of their own. And sometimes, families simply want to spend more time together without sharing a kitchen every morning. 

Some of the benefits of multi-generational living include: 

• More independence: everyone gets their own space, routines and privacy. 
• Family is nearby: company, help or childcare can be just a few steps away when you need it. 
• Less upheaval: an older relative might be able to move closer without the family needing to move house. 
• Flexibility: a granny annexe can adapt as a family's needs change over time. 
• Shared costs: living closer together can make some household expenses easier to manage. 

The trick is getting the balance right. A good granny annexe should make it easy to spend time together and close the door when everyone needs a bit of space. 

In most cases, yes. You’ll need planning permission for a granny annexe if you're creating a new, self-contained living space with its own kitchen, bathroom and bedroom.

But there can be exceptions. Since it was introduced in 1960, the Caravan Act has helped make creating a granny annexe easier for lots of homeowners, allowing them to bypass planning permission as long as the structure meets the criteria. This includes height, how it’s used, whether it can move and its connection to the main property.

Planning rules can change between areas, so it's worth speaking to your local planning authority before you start any work. They can tell you what applies to your project and whether you'll need to make a planning application.

If your granny annexe doesn't need planning permission, you can apply to your local council for a Lawful Development Certificate.

This isn't the same as planning permission, and you don't have to get one, but it can be worth doing it for peace of mind as it gives you paperwork to show that the annexe was built lawfully – and could be helpful if you decide to sell your home in the future.

A granny annexe should work for whoever is living there right now, but it's worth thinking about what they might need in the future, too. A few thoughtful design choices at the start could save you from making bigger changes later. 

If you're creating a granny annexe for an older relative who has accessibility needs, you could think about: 

• Step-free access at the entrance and between rooms 
• Wider doorways with plenty of room to move around 
• A walk-in shower rather than a bath or raised shower tray 
• Grab rails in helpful places such as the bathroom 
• Easy-to-reach storage, sockets and switches 
• Enough space to move around comfortably if their needs change 

Comfort matters just as much. Try thinking about heating, ventilation and daylight early on, rather than treating them as finishing touches. For example, if you have limited wall space in your structure, a roof window could help you draw in light from above and make the space feel brighter and roomier.

The place you build your granny annexe in depends on the space you have, your budget and how you want it to function. 

Popular choices include: 

• In the garden: a separate annexe can offer the most privacy while keeping family a short walk away. 
• As a side or rear extension: attaching the annexe to your home makes it easier to move between the two spaces. 
• In a converted garage: if you already have a usable structure, a garage conversion into a granny annexe could be a great use of space. 
• Within your existing home: reworking part of your home can create a separate living space without having to build from scratch. 

It's all about finding that sweet spot: close enough to be there when you're needed, with enough separation for everyone to still feel independent.  

There’s no one-size-fits-all answer when it comes to the cost of a granny annexe. You could spend anywhere from £52,000 for a compact space or upwards of £155,000 for a larger building – but don’t let these numbers put you off. Straightforward conversions could cost much less, so it’s always worth getting a building quote – or a few – to get a feel for rates.

Before setting your budget, check whether your quote includes things like planning and professional fees, foundations, drainage, electricity and water connections, kitchen and bathroom fittings, and landscaping. You might also want to leave some money aside for anything unexpected.

Creating a granny annexe and knowing your loved ones will be closer can be very exciting, but there are also a few tax and legal details worth understanding, especially if you're building for a relative or thinking about what might happen to the space in the future.

A granny annexe can have its own Council Tax bill, but discounts and exemptions are available in some circumstances. Exactly what you're entitled to will depend on how the annexe is used and who lives there, so we recommend checking with your local council once you know your plans.

A granny annexe can also affect the Stamp Duty Land Tax you pay when buying a property that already has one. 

Until June 2024, buyers purchasing more than one qualifying dwelling in the same transaction could sometimes claim Multiple Dwellings Relief. That relief has now been removed for most work completed on or after 1 June 2024. 

Stamp duty can get complicated, so if you're buying a home with a granny annexe, it's worth getting advice based on the property and your circumstances rather than trying to calculate it yourself.

If the annexe was approved as ancillary accommodation to your main home, they are generally treated as one property rather than two separate homes. But if you want to sell or rent the annexe out as a separate dwelling later on, you might need to apply for planning permission or have existing planning conditions changed. Your local authority can tell you what applies to your property. 

There’s a lot to think about when building a granny annexe, so it’s easy for things to get missed. A little planning early on can save you time and money, and help you create a space that’s adaptable with your family for years to come. 

Here are some of the most common mistakes to avoid: 

• Assuming you won’t need planning permission: permitted development doesn’t automatically apply to every granny annexe, so check before making any firm plans. 
• Designing first and checking the rules later: find out what’s possible for your property before making a call on a particular size, position or layout. 
• Budgeting for the build alone: consider professional fees, groundwork, utility connections, fittings and a little more for unexpected costs. 
• Only thinking about what works today: step-free access, wider doorways and an easy-to-use bathroom might not feel essential now, but could make a big difference later – especially for any ageing family members. 
• Leaving daylight and ventilation until the end: think about where light and fresh air will come from while you're planning the layout – that’s much easier than trying to squeeze in extra windows once everything else is decided. Our roof window size guide can help you find an option for your granny annexe that you (and your family) will love. 

If a granny annexe feels like the right option for your family, try using this quick checklist to kick off your project: 

• Work out what you want the space to do: who will live there? How much independence do they need? And what would make everyday life and accessibility easier for them, such as step-free access.  
• Speak to a professional: find a planner or builder who specialises in granny annexes. They can look at your property, work out what’s possible and help you understand the planning route before you go into the finer details. 
• Think about light: daylight can have such a huge impact on everyday life. If there’s a room your loved one will spend a lot of time in, could you maximise the light coming in with a VELUX roof window or flat roof window, and protect the space from getting too hot in the summer with anti-heat blinds? Making a call on this upfront will help you create a space that’s bright, fresh and comfortable to live in. 
• Set your timeline: granny annexes can take several months to move from initial ideas through planning, design and construction, and more complicated projects could take longer. Decide on a timeline or set a goal, and you can start working towards it. 

Want to dig into some inspiration first? Discover how light and ventilation can transform your home, from climate control in smaller structures to creating sun-drenched family spaces.