Radon, a colourless and odourless gas, poses a significant risk to health in areas of the UK sited on or close to igneous rock. Since the early 1980s the National Radiological Protection Board (NRPB) has been conducting an extensive monitoring programme of radon levels in dwellings and workplaces. The exposure of occupants to radon is influenced by the level of ventilation, with the trend towards energy efficiency including reduction of air change rates bringing an unwelcome rise in radon concentration.

This paper describes the effect of measures taken to increase natural ventilation rates on radon levels within a house of traditional construction on the south east edge of Dartmoor. A series of measurements was conducted by the NRPB over a period of ten years using passive detectors. The first gave an annual average of 204 Bqm-3, just above the governments current 'action level'.

Measures taken to reduce radon levels by natural ventilation reduced the annual average recorded in the final test to 110 Bqm-3. Subsequently the house was comprehensively surveyed using an Alphaguard radon meter providing a more detailed analysis of the radon levels in each room. Problems due to the ingress of radon from the drink water supply were also investigated. Plans to incorporate a positive ventilation system are discussed.