Pre- and postconstruction radon measurements in a new housing development.

Results from pre- and postconstruction radon measurements in a new housing development are presented. The houses were built in an area that had not been previously associated with elevated indoor radon concentrations. Exhalation measurements of gravel and stone from the site and soil gas measurements under several houses did not indicate an elevated radon potential. However, 4 of 21 finished houses (or 19%) exhibited annual average indoor radon concentrations over 200 Bq.m-3 (5.4 pCi/l). The highest concentrations were observed in the first house built and in 1 of the 6 houses built differently than the original designs, with the elements of a subfloor ventilation system included for possible radon control if necessary. These results suggest that site investigations can be of limited value in determining where not to include radon protection measures in new housing. Also, that care must be taken to adequately inform everyone involved in the building process of the importance of maintaining a tight seal against the ground to prevent possible radon gas entry into a house.