Radon measurements in 12,000 Swedish homes

Radon daughter levels have been monitored in 12,000 Swedish dwellings during the last two years. In 1979 the Swedish Government introduced temporary limits for the radon daughter concentration in dwellings. For existing buildings this limit is 400 Bq/m³ (0.11 WL). Two different methods were used to monitor the radon daughter concentration. The majority of the houses presented in this paper were monitored using a track-etch detector; some houses were tested using a filter sampling technique while the ventilation rate was determined. Close to 15% of the investigated houses have a radon daughter concentration higher than 400 Bq/m³. The majority of these houses were one-family houses. Almost 10% of this group has a concentration above 1000 Bq/m³ (0.27 WL). The results from this study show that the two most important sources for radon in buildings are building materials and the ground.