Several problems can be encountered following conversion of a basement in an older property into habitable accommodation: the most serious is probably dampness because early forms of basement construction had no damp-proofing. Although basements used as kitchens and servants' rooms were reasonably dry, many others suffer from penetrating dampness, mould growth and deterioration of timbers. This is unacceptable for habitable rooms. This Good Repair Guide gives advice to builders and householders on ways of treating dampness in basements by treating internal surfaces. 6 pages.