The short answer
Not as a rule. A garden room put up without permission is allowed because it is for uses such as an office or hobby room. Sleeping there, with a kitchen and bathroom, needs planning permission and building regulations approval as an annexe.
It is a question families ask once a parent’s house goes on the market: the garden room is already there, it is warm and dry, so could Mum or Dad move in? Sometimes the answer can become yes. It rarely is on the day you ask.
Why the garden room was allowed in the first place
Most garden rooms are built without a planning application, under the permitted development rights for outbuildings. Those rights cover buildings used for purposes incidental to the enjoyment of the house. The government’s guidance gives examples such as a home office, a gym, a hobby room or storage.
The same guidance says that a bedroom, a kitchen or a bathroom is primary living accommodation, not incidental. A garden room that someone sleeps in, cooks in and washes in has moved outside the rights it was built under, whatever its size.
The building regulations side
Most garden rooms were also exempt from building regulations. A detached single-storey building under 30 m² is exempt as long as it has no sleeping accommodation, and is either a metre or more from the boundary or built mostly of non-combustible materials.
The exemption goes the moment someone sleeps there. The building then has to meet the regulations for somewhere to live: insulation, ventilation, fire safety and means of escape, drainage and electrics. Most garden rooms were not built to that standard.
What happens if someone moves in anyway
Councils usually find out through a council tax enquiry, a neighbour or a sale. They can then ask for a planning application, and if it is refused, take enforcement action to stop the building being lived in. When the house is sold, the buyer’s solicitor will ask about it, and an unapproved bedroom in the garden can hold up the sale.
There is also the practical side. A building that is cold in January, has no fire alarm and no second way out is not a safe place for an older person to sleep.
Turning a garden room into an annexe properly
If the building is sound, it can sometimes be brought up to standard.
- Ask a surveyor or a building control body to look at it. The questions are whether the walls, floor and roof can take more insulation, and whether the foundations are adequate.
- Apply for planning permission for use as an annexe to the main house. Expect a condition that it stays part of your household.
- Get building regulations approval for the conversion. If work has already been done, ask your council about a regularisation certificate.
- Add the services properly. Waste water is usually the hardest part; a shower and kitchen need a connection to the house drains or a pump.
Sometimes the honest answer is that the upgrade costs nearly as much as starting again with a building designed as an annexe. Before deciding, compare both. Our granny annexe cost calculator gives a national guide for a new annexe of the same size.