Guide
Do you need planning permission for a garden room?
Most garden rooms fall under permitted development, which means no application. The limits that catch people out are height, boundary distance and how the building is used.
The usual position
A garden room is normally treated as an outbuilding and falls under permitted development, so no planning application is needed, provided it meets all of the conditions rather than most of them.
The main ones: single storey, no more than 2.5 metres high if it sits within two metres of a boundary, no more than 3 metres high with a flat roof or 4 metres with a dual-pitched roof elsewhere, no verandas or balconies, behind the front elevation of the house, and covering no more than half the land around the original house.
Where it stops being permitted development
Sleeping accommodation is the big one. A garden room used as an annexe, a guest bedroom or anything self-contained is generally not permitted development and brings building regulations with it. Occasional use by a visitor is a different question from creating a separate dwelling.
Listed buildings and conservation areas have tighter rules, and land in front of the house is usually out. Some properties have permitted development rights removed by a planning condition, which is common on newer estates and is worth checking on the title.
Building regulations are a separate question
Planning permission and building regulations are different systems. A garden room under 15 square metres with no sleeping accommodation generally needs neither. Between 15 and 30 square metres it is usually exempt if it is at least a metre from any boundary or built substantially of non-combustible material. Over 30 square metres, or with sleeping accommodation, building regulations apply.
The electrical supply is notifiable work regardless, and needs an electrician who can certify it.
How to be sure
The council's planning department will confirm, and many will do it informally. A Lawful Development Certificate costs a fee and gives you a formal document saying no permission was needed, which is worth having when you sell. Do not rely on a supplier telling you it is permitted development; they are not the ones who deal with an enforcement notice.
Common questions
Can I sleep in my garden room?
Occasional use is one thing; using it as self-contained sleeping accommodation generally takes it outside permitted development and triggers building regulations.
How close to the boundary can it be?
Any distance, but within two metres of a boundary the maximum height drops to 2.5 metres overall, which rules out most pitched roofs.
Do I need building regulations approval?
Usually not under 15 square metres without sleeping accommodation. Over 30 square metres, or with a bed in it, yes. The electrics are notifiable either way.