With an ageing population and rising care costs, more and more families are considering granny annexes as an alternative solution
It means that your family member can be close by, but still retain their independence, while you both keep your own space
Whether you’re looking after an elderly parent or creating a separate living space for a grown-up child, a granny annexe could be exactly what you need.
Here’s everything you need to know.
What Is a Granny Annexe?
A granny annexe is essentially a self-contained building in your garden. It’s usually considered a dwelling, as to be completely independent, it’ll need a bathroom and maybe even a small kitchen with running water. Of course, you could opt for something without plumbing and the family member can just use the facilities in the main house.
These additions can be for anyone, not just grandparents, and can make for a good spot for adult children to hunker down while they save for a deposit for their own home.
Types of Granny Annexe
There are several ways to create a granny annexe, each with different costs, timescales, and planning implications:
Attached annexes are built as an extension to the main home, sharing a wall. They tend to be popular, as extensions can add value to a home.
Detached annexes are standalone structures in the garden, completely separate from the main house. These offer maximum privacy and independence and are often built using timber frame, modular, or traditional brick construction.
Converted outbuildings make use of existing garages, barns, or workshops. Depending on the structure, these can be a cost-effective route, although that’s not always the case and significant renovation is often needed.
Garden rooms with residential use are a growing trend, where a high-spec garden building is fitted out as a place someone could feasibly live in. This is where planning rules become particularly important.
Planning Permission: What You Need to Know
One of the most common questions around granny annexes is whether planning permission is needed. The answer depends on several factors, including the type of structure, its size, and how it will be used.
Permitted Development Rights
In lots of cases, smaller detached structures in the garden, including some garden rooms, can be built under Permitted Development (PD) rights, meaning you don’t need a formal planning application.
For a garden building to qualify under PD, it must generally:
- Be single storey with a maximum eaves height of 2.5 metres
- Not exceed 4 metres in overall height (or 3 metres with a dual-pitched roof)
- Not cover more than 50% of the garden area
- Not be positioned forward of the principal elevation of the house
- Not be used as a separate dwelling
That last point is crucial. If the structure is intended for use as self-contained residential accommodation with its own cooking and sleeping facilities, it’s likely to be treated as a separate dwelling by your local planning authority, which triggers the need for full planning permission, regardless of its size.
When Full Planning Permission Is Required
You will almost certainly need to apply for planning permission if:
- The annexe is detached and intended for permanent residential occupation
- The structure is in a conservation area, Area of Outstanding Natural Beauty (AONB), or listed building curtilage – where PD rights are more restricted
- The total footprint exceeds PD thresholds
- The annexe includes a self-contained kitchen
It’s worth noting that planning authorities generally look more favourably on annexes that are ‘ancillary to the main dwelling’, which basically means they serve the household rather than functioning as a wholly independent property.
Conditions are sometimes attached to planning approvals to ensure the annexe remains in use by a family member and not turned into a business.
Building Regulations
Separate from planning permission, any new habitable structure must comply with Building Regulations, covering structural integrity, fire safety, insulation, ventilation, and energy efficiency. This applies whether or not planning permission is required.
The Benefits of a Granny Annexe
Beyond the practical and financial advantages, granny annexes offer real emotional benefits. They allow elderly relatives to maintain independence and dignity while being close enough for support. It also means you’re not out of pocket for care costs if you can manage care between family members.
They can also add value to your property; a well-built, high-quality annexe is an increasingly attractive feature for buyers.