Do I need to comply with building regulations for a garage conversion?

Almost always, yes, even when planning permission is not required. Building regulations for garage conversions cover structure, fire safety, damp and moisture, ventilation, insulation and electrical safety, and they apply whenever you turn a garage into a habitable room. You will usually submit either a building notice or full plans application, and building control issues a completion certificate at the end. Skipping this can cause problems with insurers and when you come to sell, so a straightforward garage conversion should always comply with building regulations.