This 3-Part Good Repair Guide offers guidance to builders and homeowners carrying out various works to reduce radon levels in homes. Part 1 covers the installation of natural and mechanical (fan-assisted) ventilation to underfloor spaces. Part 2 gives guidance on positive ventilation systems. Part 3 covers the installation of active and passive sump systems. This 3-Part set replaces the guidance given in BRE Reports BR 270, BR 281 and BR 227.