Ventilation and radon transport in Dutch dwellings: computer modelling and field measurements.

In 1995 and 1996 radon concentrations and effective air flows were measured in approximately 1500 Dutch dwellings built between 1985 and 1993. The goal of this investigation was to describe the trend in the average radon concentration by supplementing the first survey on dwellings built up to 1984 and to quantify the contributions of the most important sources of radon. In the living room of new dwellings the average radon concentration was 28 Bq m(-3), which is 50% higher than in dwellings built before 1970. Measurements of effective air flows showed the most important source of radon in the living room of new dwellings to be the building materials, with an average contribution of 70%. The other 30% comprised outside air and air from the crawl space in equal quantities. The long-term increase in the indoor radon concentration is mainly due to improvements in insulation since 1970, resulting in a fourfold decrease in infiltration through the building shell. Model calculations, supplementing the field measurements, confirmed the dominant effect of increasing airtightness of dwellings compared to effects of the observed trend in the use of building materials.