Single-storey outbuildings can be considered as permitted development; without needing planning permission. Located to the rear or side of a property, they must be ancillary to the main dwelling and not contain living accommodation – office/studio space for example.
The footprint can be up to 50% of the total area of land around the house. The maximum height for a dual pitch roof is 4m (3m for other roof types [e.g. mono pitch or flat]), and 2.5m if within 2m of the property boundary. Building regulations approval is not usually required up to 30m2 in floor area (no sleeping accommodation). More information can be found at www.planningportal.gov.uk