Confused by building regulations for annexes? I asked the pros to clear up when approval is and isn’t needed

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Building regulations can be a minefield for any project - but do they apply where annexes are concerned?

The world of building regulations for this type of space can be complex. Ultimately, the answer depends on how you intend to use the space. To help give you an idea, I've asked the experts to break down when an annexe needs to meet building regulations and when it doesn't. But as these rules can depend on where you live, it's always best to double check with Local Authority Building Control before you start work to make sure you stay on the right side of the rules.

Do building regulations apply to an annexe?

Whether you need building regulations approval for your annexe will depend on its intended use and its size (Image credit: Future PLC)

Rules and regulations for annexes is a murky world, and specifics of what the space will be used for will ultimately inform the consent you need in terms of both building regulations and planning permission for an annexe.

'The name itself isn’t what matters most, what really counts is how the space will be used,' explains James Home, founder of Okopod. 'If it’s a self-contained space, like an annexe or granny flat, with a kitchen, bathroom, or sleeping area, then it’s classed as habitable, and that usually means you’ll need full planning permission and Building Regulations approval.'

However, as Jo Berrington, director at The Garden Room Guide, explains: 'There is an alternative route under the Caravan Act, where the annexe is classed as a mobile home. In these cases, Building Regulations approval isn’t required, but buyers will still need to obtain a Certificate of Lawful Development to confirm that the structure is legally permitted on the site. This route has some restrictions — the building must remain movable and be used in a way that's incidental to the main house, not as a rental or business premises.'

Building regulations for habitable annexes

'In most cases, if you’re building an annexe, full Building Regulations will apply because it’s considered habitable accommodation,' adds James Home. 'That means the structure needs to meet a wide range of standards covering:

• Part A – Structural safety
• Part B – Fire safety
• Part F – Ventilation
• Part L – Energy efficiency
• Part H – Drainage and waste
• And possibly others, depending on the design and use'

Building regulations for non-habitable annexes

If your annexe isn't going to be used as living accommodation, and is less than 30m2, then building regulations approval is not usually require, but it's always best to check with LABC before you start building (Image credit: Okopod)

James Home continues: 'For outbuildings like sheds, home offices, or garden rooms that aren’t used for as liveable spaces, there may be exemptions, especially if they’re under 30 square metres, single-storey, and made from non-combustible materials. The safest approach is to speak to Building Control early in the process so you know exactly what’s required for your specific build.'

FAQs

What kind of building regulations application do I need?

If your annexe is going to be 'habitable', then you will need to get building regs sign off (Image credit: Okopod)

There are two types of building control applications. The first, a Full Plans application, will review your plans before any work begins. It is most expensive upfront, but might save any expensive remedial work being carried out further down the line.

The second type of application is a Building Notice. If your annexe is uncomplicated and you trust the work will be completed complying with the regulations, you can fill this application and begin work after 48 hours.

Which type of application you choose is ultimately your choice based on speed and budget, but as a general rule of thumb, I would suggest a Full Plans application for habitable spaces, especially those with heating, lighting and a bathroom or kitchen.

Who is responsible for ensuring building regs compliance for an annexe?

Many custom-build annexe companies might offer to take on the building control application on your behalf, but when it all comes down to it, you as a homeowner need to ensure the work complies with building regulations. And even if your annexe provider makes the application on your behalf, you still may have to complete and sign a declaration as the customer.

'Ultimately, the homeowner is legally responsible, but in practice, most people choose to work with a specialist company that handles the entire process on their behalf,' says Jo Berrington. 'We always recommend confirming who is responsible for each stage of the process before committing to a build — particularly if multiple contractors are involved.'

If you choose to take on the responsibility of applying for building regulations yourself, you can either contact your local authority building control (LABC) directly, or use a private company. The latter will be more expensive, but might ensure your project runs smoother than having to wait for the LABC to make a home inspection visit.

What can happen if you don’t get building regs approval for your annexe?

Neglecting to obtain building regulation approval where it is deemed necessary is a very serious issue. The LABC can demand the work is altered and made compliant, is taken down entirely, or for you to pay a hefty fine.

If you want to move house in the future, trying to sell a property without the necessary certifications and documentation might prove tricky and could reduce your home's value as a consequence.

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If you're as yet undecided about how best to use your new space, these garden room ideas might help you decide.