BRE inspections of rehabilitation work in progress have revealed instances of inadequate separating walls between dwellings, including half brick or brick on edge, large gaps or absence of walls in roof spaces, and holes alongside floor joists or other timbers built into the walls. The principle of sound insulation is to ensure that the resistance of separating walls is satisfactory by blocking all holes or by constructing an independent leaf. This Good Repair Guide gives guidance to builders, householders and landlords on diagnosing a sound insulation problem and deciding on remedial action. There is also advice on sound insulation for flat conversions. Part 1 (6 pages) covers diagnosis of the problem and lining walls with plasterboard and a sound absorbent quilt, and Part 2 (4 pages) covers remedial action such as building an independent ceiling or a floating floor. It also briefly covers legal solutions for dealing with noisy neighbours.