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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. But before you embark on a project to build your relatives their own home in your garden, you need to consider planning permission, council tax and costs.
An annexe is a self-contained unit that’s either joined onto or adjacent to a main and usually larger building. In most cases, it will offer a degree of independent living that gives it the feel of the occupier’s own space and contain a living area, kitchen, bathroom and bedroom.
Granny annexes are increasingly popular. According to recent figures from the Valuation Office Agency there are around 60,000 annexes in England and Wales alone.
There’s no law requiring you to hire an architect to create a granny flat. A builder should be able to propose a design for you that does the job.
Alternatively, an experienced architect will be able to talk through what you are trying to achieve from your granny annexe and deliver a design that meets those needs. They will also be able to handle your planning application.
What’s more, having a design expert on board means you get the maximum amount of space and style for your budget. This means, if you sell your home in the future, you’ll get the best returns for your investment. Find out how much fees may cost in our guide Architect fees and how to cut them.
Find Architects near you, discuss your project and get quotes.
Granny flats cost around £90,000 on average for a new, detatched building, according to Checkatrade. But the price will vary depending on…
One of the cheapest ways to build a granny flat is to converting a garage or existing outbuilding to create your granny annexe. This could shave a significant amount off your budget.
Alternatively, buying a prefabricated granny flat should also cut costs significantly. Be aware that you should try to keep the granny annexe near your main building. Over 10ms away and it’s unlikely you’ll be able to connect to your mains.
Based on how and where you plan to build your granny annexe there will be different requirements for planning permission, so it’s always best to seek professional advice and check with your local planning office.
However, in some cases you may be able to avoid the need for planning permission, for example if you can build your granny flat within your permitted development rights.
It’s also possible to build a granny flat without planning permission by using the Caravan Sites Act, (which is not just about caravans, but effectively the definition of a mobile home in general).
Speak to a Planning Consultant in your local area today about your project
If the granny annexe is occupied by a dependent relative, such as an elderly parent or a disabled family member, and forms part of the same overall property, it may be exempt from council tax.
Alternatively, you may be able to get a 50% council tax discount if the granny flat or annexe is lived in by a relative or resident of the main house. In both cases you should speak to your council to discuss your individual circumstances.
You’ll need to contact your local authority and tell them your situation. Find out more in our guide Can I get a council tax reduction?
There are many advantages of building a granny flat, including:
Granny flats can offer an elderly relative somewhere to call home that offers them independence but comes with the added benefit that you will be on hand for company and support.
If living in a granny annexe means you can avoid your elderly relative going into a care home, not only will it mean they’re close by but it could also save a huge amount of money too. Residential care costs an average of £60,000 a year while nursing home care costs an average of £73,000 a year. So it could be a major saving. Find out more in our guide How to avoid selling your house to pay for care.
Being able to spend more time together may improve family relationships and allow grandparents to spend more time with grandchildren. If able, they may also take a bigger role in looking after children too such as in school holidays.
Given the huge cost of getting on the property ladder, building an annexe that adult children can live in while they save up for a house deposit may be a good option as it will offer you and them their own space.
Some people build a granny flat, planning to rent it out to a lodger or on sites like AirBnb until they need to use it. It could be a handy form of extra income. But make sure you do your research first. Read our guide on Renting out a room in your house.
Building a granny flat could increase the value of your home by up to 20%-30%, according to Checkatrade. But the amount will depend on many factors including size of the granny flat, finish and location.
Find local builders with our partner the Federation of Master Builders.
But there are some downsides to consider too, such as:
If you’re building a granny flat in your garden rather than converting part of your existing house like your garage, you’ll lose garden space. So it’s important to consider this when you’re deciding whether or not to build a granny flat and the size too.
While having your loved ones living close by may bring benefits, there is the risk of friction from spending more time together. Have an open conversation first about what each of your expectations are so you’re on the same page from the start.
By law, any building, or part of a building, which has been constructed or adapted for use as separate living accommodation must have its own council tax banding banding. A self-contained unit can mean both a living space that’s separate from other accommodation, as well as living accommodation that’s connected to and shares access with adjoining accommodation, for example an annexe for an elderly relative. Find more details on Council tax bands and self-contained units on this VOA factsheet.
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