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 about 1500 Dutchdwellings built between 1985 and 1993. The goal of this investigation was to describe the trend inthe average radon concentration by supplementing the first survey on dwellings built up to 1984and to quantify the contributions of the most important sources of radon. In the living room of newdwellings the average radon concentration was 28 Bq m-3, which is 50% higher than in dwellingsbuilt before 1970. Measurements of effective air flows showed the most important source of radonin the living room of new dwellings to be the building materials, with an average contribution of70%. The other 30% comprised outside air and air from the crawl space in equal quantities. Thelong-term increase in the indoor radon concentration is mainly due to improvements in insulationsince 1970, resulting in a fourfold decrease in infiltration through the building shell. Modelcalculations, supplementing the field measurements, confirmed the dominant effect of increasingairtightness of dwellings compared to effects of the observed trend in the use of building materials.