It depends on the size and use. A garden room used as non-habitable space (home office, gym, studio) under 25m² is generally exempt from planning permission, provided it sits behind the building line and you retain at least 25m² of private open space to the rear. Habitable units, granny flats, and anything used for sleeping or rented accommodation typically require planning permission or fall under specific exemptions like the Rent a Room scheme. We always recommend confirming with your local authority before ordering, and our team can guide you through what applies to your site.