Radon concentrations in wooden houses

Japanese houses which had been adapted to the hot and humid of summer, are different from western houses regarding air tightness. Especially in the last two decades, many Japanese people live in houses having high air tightness, built with inorganic materials. Excessive usage of aluminum framed sliding-doors increases the air tightness inside wooden houses, allowing the radon emanates into the air tightened rooms from the soil under the crawl-space as well as from a kind of gypsum used for heat insulation. In order to determine the potentially harmful environmental conditions, the diffusion behavior of radon in Japanese wooden houses was assessed and the properties of wood and wood-based materials as radon sealants were investigated. The annual mean concentrations of radon in the crawl-space were 34 Bq m(-3). The concentrations in the first and the second floors were lower than that in the crawl-space. This fact shows that the main source of radon in the wooden houses is the soil under the crawl-space. In any board thickness of Spruce, the reduction rates in the tangential direction was 90 % or more. It was made clear that wood has good properties as a radon sealant.