Abstract: Apparatus for inhibiting ingress of radon into a room (20) of a building (1a, 1b), the room is at least in part below ground level, the apparatus comprises a waterproofing structure (10), the waterproofing structure defines with at least one of an adjacent wall, floor and ceiling a cavity (11) therebetween, and the cavity is sealed from the interior space of the room, and the apparatus further comprises at least one of a positive pressure pump (8) to apply positive air pressure into the interior space and suction apparatus (7) which is in communication with the cavity.