The effect of different foundation systems against fungal flora in the crawl space of a new wooden Japanese house
A Toyoumi, S Horisawa, T Yoshimura, S Doi,Y Imamura
In order to establish novel preventive measures against damage of wooden houses by decay fungi with less-use or no-use of chemicals, we periodically monitored the fungal flora in the crawl space of a new wooden Japanese house build with recyclable and low-environmental load materials at the Research Institute for Sustainable Humanosphere, Kyoto University. We employed either a layer of concrete or just soil as the foundation system of the crawl space of the model Japanese house. Moisture content of Sugi foundation timbers and temperature & humidity of the crawl space with different foundation systems were measured as well as the sampling of fungi by the following methods: a) from the crawl space atmosphere with a PDA plate, b) from foundation timbers with a soft transparent plastic tape, and c) from small wood blocks laid on a layer of concrete or on soil. Fungi, which were visually estimated to be basidiomycetes, were also identified with DNA-based methods. Then a monoculture decay test was conducted with these fungi. Numbers of fungal colonies grown from the concrete foundation samples were significantly lower than those from the soil foundation samples. Over the year the soil section generally showed higher humidity and moisture content 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 than in the concrete section. Most of isolated basidiomycetes were white rot fungi with the exception of a brown rot fungus, Fomitopsis pincola. The majority of the white rot fungi were Trametes vesicolor. In order to analyze effect of soil on the fungal flora, all ventilation slits were air-tightly closed with aluminium tape for each crawl space section after all the sampling was completed. This resulted in higher colony forming unites (CFUs), humidity and moisture content of foundation timbers. This study clearly indicated the close relationship between the risk of wood decay and the foundation system in wooden Japanese houses, and the higher decay risk in the soil section than in the concrete section.
Keywords: wood-relating fungi, crawl space environment, foundation system