In 40 seconds
A typical garden room costs £10,000–£30,000 supplied and fitted in 2026, and most fall under permitted development — meaning no full planning application is needed. To stay permitted, an outbuilding is usually single storey, no more than 2.5m to the eaves and 3m to the ridge (4m for a dual-pitch roof), set back from the front of the house, and not covering more than half the garden. The catch: it must be incidental to the house. The moment a garden room becomes self-contained living or sleeping accommodation, it generally needs full planning permission and Building Regulations approval. Rules vary locally and permitted development can be removed by an Article 4 direction, so always confirm with your Local Planning Authority. Get at least three itemised quotes from a garden room builder, and check the specification covers insulation, foundations and electrics — not just a glorified shed.