A garage conversion transforms an underused garage into habitable living space, like a home office, gym, or playroom, by adding insulation, flooring, windows, and converting the garage door opening, often without needing full planning permission if kept internal, but always requiring Building Regulations approval for safety, and it's a cost-effective way to add square footage without a full extension. Key steps involve planning, checking local rules, structural work, damp-proofing, insulating, installing utilities (electrics, plumbing), finishing walls/floors, and decorating.