An Evaluation of WUFI-Bio to Predict Mold Growth in Straw Bale Walls in Japan

Abstract

The greatest challenges facing straw bale building in Japan, and many other countries with high humidity and precipitation, are moisture and the susceptibility of straw to microbial decay. WUFI-Bio, developed by the Fraunhofer Institute for Building Physics, is a computer program that assesses the risk of mold growth in buildings based on measured or computed climatic conditions. Researchers in Japan have monitored the hygrothermal conditions of six straw bale buildings in Japan and evaluated the risk of mold growth based on an interstitial temperature and relative humidity guideline. The purpose of the present study is: (one) reevaluate the potential for mold growth in the six buildings using WUFI-Bio and (two) evaluate the accuracy of Holzhueter and Itonaga′s interstitial temperature and relativity guideline vis-à-vis WUFI-Bio. As a result of the study, the potential for mold growth was found to vary by structure. Buildings utilizing rainscreens were found to have a lower risk of mold growth. Holzhueter and Itonaga′s interstitial temperature and relativity guideline was found to over exaggerate the potential for mold growth. Also, although Holzhueter′s guideline does indicate a potential for mold growth, the number of hours above the guideline alone is not a sufficiently accurate indication of severity.