59
VENTILATION AND RADON TRANSPORT IN DUTCH DWELLINGS:
COMPUTER MODELLING AND FIELD MEASUREMENTS

Johan Lembrechts, Martien Janssen and Paul Stoop
RIVM, Laboratory of Radiation Research
PO Box 1, NL-3720 BA Bilthoven, The Netherlands
phone: 00-31-30-2742294 fax: 00-31-30-2744428 E-mail: johan.lembrechts@rivm.nl

In 1995 and 1996 radon concentrations and effective air flows were measured in about 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.
Keywords: indoor radon, survey, airtightness, ventilation, occupant-behaviour, building material