Usually not — garden rooms are treated as outbuildings, and outbuildings are one of the more generous corners of permitted development. The moment you try to live in one, however, the answer changes completely, and that is where most of the trouble starts.
The outbuilding limits
To be permitted development, a garden room must be single storey, sit to the rear of the principal elevation, and take up no more than half the land around the original house alongside everything else you have built. Maximum overall height is four metres for a dual-pitched roof and three metres for anything else, with eaves no higher than two and a half metres.
The catch that trips people is the boundary. If any part of it sits within two metres of a boundary, the entire building is capped at two and a half metres high. Not the bit near the fence — the whole thing. Plenty of garden rooms are designed at three metres and then shuffled two metres off the fence at the last minute for exactly this reason.
Where "incidental" becomes "dwelling"
Permitted development covers outbuildings incidental to the enjoyment of the house. A home office, a gym, a studio, a playroom, somewhere to put the drum kit — all comfortably incidental.
What is not incidental is self-contained living accommodation. Add a bedroom, a kitchen and a bathroom, and you have built a dwelling in the garden. That needs full planning permission, and it will be assessed on entirely different grounds. A shower room for a garden gym is generally fine; a shower room next to a bed and a hob is a granny annexe with a different name on the drawings.
The usual exceptions
- Listed buildings — listed building consent needed regardless
- Conservation areas, AONBs and national parks, where outbuildings to the side of the house lose permitted development rights
- Estates where permitted development rights were removed by a planning condition — check the original approval, not your deeds
- Anything forward of the principal elevation
Building regulations
A garden room under 15m² internal floor area generally does not need building regulations approval. Between 15m² and 30m² it can still be exempt if it is at least one metre from any boundary or built substantially of non-combustible material. Over 30m², or if you are sleeping in it, building regulations apply. Electrics installed out there are notifiable work whatever the size.
Get the certificate
Same principle as every permitted development project: not needing permission is not the same as being able to prove it. A Lawful Development Certificate is what a buyer's solicitor asks for, and it is far easier to obtain now than to argue from memory in eight years. Our PD Compliance Pack assesses eligibility and produces the application for a fixed £650.
If it turns out you need full permission — because of the living accommodation, the location, or a removed right — the Standard Planning Pack is the same fixed fee. Either way you get existing and proposed plans and elevations, a site plan and a location plan, back in 7–10 days. Send us the dimensions or ring 0114 463 0090 and we will tell you which one you are on.