The effect of different foundation systems on the fungal flora in the crawl space of a new wooden Japanese house

To establish novel preventive measures against damage of wooden houses by decay fungi with less chemical, we periodically monitored the fungal flora in two different foundation systems in the crawl space of an experimental Japanese house. We employed either a layer of concrete or just soil as the foundation system. Moisture content of foundation timbers, temperature and humidity of the crawl space were measured. Fungi were sampled by the following methods: a) from the crawl space atmosphere with a PDA plate, b) from foundation timbers with a soft plastic tape, and c) from small wood blocks laid on a layer of concrete or on soil. Visually basidiomycetes were served for DNA analyses. A decay test was conducted with these fungi: 16 white rot and a brown rot. Numbers of fungal colonies in the concrete section were lower than that in the soil section. The soil section generally showed higher humidity and moisture content of foundation timber than the concrete section. These findings suggested that the soil strongly influenced the water condition of the crawl space, indicating the higher decay risk in the soil section. In order to analyze the effect of air-flow on the fungal flora, all ventilation slits were air-tightly closed with an aluminium tape. This resulted in higher numbers of fungal colonies, humidity and moisture content of foundation timbers in the soil section. This study indicated the importance of foundation system in wooden houses, and the higher decay risk in the soil floor than in the concrete floor.