If you’re lucky enough to have an outside space big enough to accommodate one, you may have thought about building a granny annexe in your garden in order to keep a family member close by (not necessarily Granny, but quite possibly). 

Naturally, there are lots of questions surrounding granny annexes and the pros and cons of building one. This post aims to answer the most pertinent ones for those who are considering adding more space to their home.

Let’s dive straight in with a definition first, though, shall we?

What is a granny annexe?

In short, a granny annexe is simply a secondary building away from the main house, usually in the garden, built to accommodate an elderly relative, hence the name. Although this is still a common reason for erecting an annexe, especially for those who are faced with expensive care home fees, their usage has changed considerably over the last couple of decades.

Homeowners now build granny annexes for youngsters as much as they do for elders. Building a granny annexe is particularly useful for parents whose children may otherwise struggle to get on the property ladder and it has the added benefit of increasing the overall value of the main house. Win win!

What are the planning rules for granny annexes?

Finding out if your granny annexe will require planning permission will depend upon a number of factors, not least of which is the Caravan Sites Act and whether or not your annexe is deemed to be covered by it. 

Basically, if the annexe you intend to erect is classed as a mobile home, as stated in the Caravan Sites Act, and the new building is going to be used by a family member and not put up for sale or rent separately from the main house, you may not need planning permission. 

You will, however, need to obtain a Lawful Development Certificate from your local authority to confirm the above and clarify that the annexe is deemed to be incidental, i.e. seen as another room of the main residence, but in the form of an outbuilding. 

Hiring a planning expert in such situations is always the most prudent course of action, as mistakes can be incredibly costly. Many garden annexe specialists offer a planning service included in the overall price of the build. 

How big can a granny annexe be?

The size of this additional building will also be a consideration, so how big can a granny annexe be? Well Local Planning Authority (LPA) regulations will vary from council to council, but a general rule that stands pretty much everywhere is that the annexe’s footprint cannot exceed that of the main house.

In addition to this, the LPA will likely take the combined footprints of both the annexe and the main property and look at its relation to the land you own. The higher the percentage to be built upon, the more difficult it will be to obtain planning permission for it.

How much does it cost to build a granny annexe?

Another incredibly common question is how much does it cost to build a granny annexe? As one would expect, there are a lot of variables at play here, so even a ballpark figure is difficult to arrive at.

Will you build the granny flat from scratch, or are you going to buy a pre-designed portable garden annexe? How big will it be? What build type will suit your needs best? What about fixtures and fittings? All of the above will need to be taken into consideration.

That said, as a very rough guide, you will be looking at somewhere in the region of £30k to £120k to build a granny annexe in the UK. 

What about council tax on granny annexes?

Granny annexes usually fall into one of two camps when it comes to council tax: reduced to 50% or exempt altogether. Both are dependent on a family member living in the annexe, however. If a non-family member lives in the granny flat in your garden, full council tax will apply.

The difference between a reduction and exemption largely comes down to dependency. If the family member living in the annexe is deemed to be dependent, then there will be no council tax levied. Non-dependent family members, on the other hand, will receive a 50% reduction.

That’s it for another week, we sincerely hope you found the post useful and informative. If you’d like more of the same in your inbox every Monday, sign up for our weekly newsletter

Thinking of moving to a bigger home? Or maybe downsizing? Regardless of whether you’re moving up or down the property ladder, Petty’s can help. With well over a century behind us, you’ll be hard pushed to find an estate agent with a greater depth of knowledge, and our family-first ethos means you’ll also receive the service you deserve.

So, whether you’re buying, selling, or both, call our team today to find out what we can do for you when you make your next move.

should you build a granny flat in your garden