If an attic or loft is converted into a liveable space, such as a bedroom, Building Regulations approval is required. However planning consent is only required if the conversion will extend or alter the roof space, and it exceeds specified limits and conditions.
When buying a house with an existing attic conversion, it will be necessary to ascertain when the work was carried out and whether the necessary consents were obtained. This is often difficult if work was carried out by an earlier owner, and it may be necessary for an indemnity insurance policy to be obtained to cover any loss if the local authority takes enforcement action for removal of the conversion.
If a conversion has been carried out without building regulation consent, there is a danger that the work may have weakened the existing structure of the building, especially the roof. A building survey may indicate the existence of a conversion, and may state if a further detailed inspection is required (e.g. if the roof structure has been hidden by conversion works.)
Attics or lofts are often used as storerooms or workrooms, and the floor may have been boarded and roof windows inserted. This does not require any consent provided that the attic is not used as a liveable space.