Can I build a granny annexe under Permitted Development?

A granny annexe can provide flexible accommodation for your family – but do you need full planning permission? Find out the answer to one of our most popular enquiries right here. 

A granny annexe can provide a practical and affordable solution for homeowners to provide self-contained accommodation to members of the family that are looking for privacy and a space to call their own.

From a planning point of view, however, they are considered separately from an outbuilding, and so cannot be built under Permitted Development Rights – a common misconception.

Outbuildings considered ‘incidental to the enjoyment of the main house’, such as a shed, poultry pen, beehives, garages or a gym can reasonably be considered incidental, and therefore can be built under Permitted Development – generally because people don’t stay or sleep in them.

granny annexe

If, however, there is anyone living there on any kind of permanent basis – even if it’s a member of your family – it’s considered residential accommodation (i.e where people can sleep, wash or prepare food), and ‘not incidental to the main house’, and will require planning permission from your local council if being build from scratch. That’s not necessarily a bad thing, it just means that the application will be looked at more closely as it has to meet minimum standards for habitable spaces. 

Can I convert an existing building into a granny annexe?

Yes, you can! There is still paperwork involved in that you’ll need to complete a Change of Use application to ensure that the planning department is aware that the space is being used for habitation on a semi-permanent basis – otherwise you risk an enforcement notice and a fine. 

If you’re thinking in the long term about providing discrete accommodation in the future for your family, it would certainly be possible to construct an outbuilding for a gym with a small kitchen and a shower/WC (ideally with a Lawful Development Certificate to ensure correct paperwork).

Further down the line, as it became necessary, you’d be able to convert the gym into a granny annexe via a Change of Use application – and this is a pretty frequent scenario.

Can I turn my detached garage into a granny flat?

This is a little more complicated – some garages have covenants attached to them specifying that they have to stay as parking, so you’ll have to check your paperwork before you make plans.

If you’ve got a detached garage, you are very likely to need to apply for a Change of Use to turn it into a granny annexe, whereas attached garages can often be converted under Permitted Development Rules.

There is little consistency between councils on this and they tend to reserve the right to judge each case on its own merits, so there is no one-size-fits all answer to whether you’ll be able to convert or not under PD – although it’s unlikely.

Remember that Building Regulations are applicable to granny annexes, converted or built from scratch, to ensure they meet minimum standards.

Talk to your local authority

Lapworth Architects can offer you advice based on our own experience of converting and constructing granny annexes, however, each case must be taken on its own merits and particular conditions and location.

Given the discrepancies between different councils and frequent contradictions surrounding granny annexes, it would be wise to contact your local authority’s planning department to ensure that whatever you have planned – new build or converted granny annexe – is compliant. 

Many West Midlands councils, including Birmingham, offer some kind of free consultancy or pre-application process for homeowners to get clarity on what they can and can’t build, so take advantage of this – or ask us to do it for you!

We can cover both your granny annexe design, planning and building regulations needs, so drop us a line about your project!

Why Lapworth Architects?


Our 20+ years of work mean great design and good relationships with planning departments across the region to give our projects the best chance of getting your planning permission and starting building.


Your budget is tailored to your needs so you’re always on top of your costs. We’re proud to offer excellent value for money for our services, from design and planning right through to build.


Our breadth of knowledge makes us an efficient and sustainable choice of local architect, and we have a real vested interest in improving our own built environment right here in the West Midlands.


At whatever stage you’re at with your project, if you’re looking for honest, quality advice from professionals, chat to us, leave us a message or call us on the number at the top of the page. Let’s talk!

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