The Humidity Variation in Crawl Spaces of Japanese Houses

We found that many houses experience summer condensation in the crawl spaces. These houses are constructed in compliance with the Japanese Building Code requirements for crawl space ventilation and contain ground covers. The humidity in the crawl space affects durability of the house. We have monitored the temperature and humidity variations of 36 houses in Japan over two years and confirmed the annual variations of hygro-thermal conditions in the crawl spaces by the numerical analysis. Numerical calculations using a one-dimensional heat transfer model agreed well with the measured results.

These results show that during the summer, houses in this region of Japan have extremely high humidity in crawl spaces. The daily average of crawl space vapor pressure is nearly equal to that of the outdoors. The effects of floor thermal resistance and ground moisture are also estimated in this paper.