The Influence of Ventilated Rainscreens on the Interstitial Hygrothermal Environment of Straw Bale Walls

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. Researchers in Europe and North America have found the use of ventilated rainscreens to help control interstitial moisture in straw bale walls. The indoor, outdoor and interstitial hygrothermal environment of six straw bale structures in Japan have been monitored. The six buildings are organized into two groups. The first group includes buildings consisting of straw bales walls with an earthen or lime plastered exterior finish applied directly to the bale walls. The second group includes buildings consisting of straw bale walls utilizing ventilated rain screens. The purpose of the present study is: (one) evaluate the potential for mold growth in the six buildings, (two) clarify moisture dynamics, and (three) determine the effectiveness of ventilated rainscreens to control moisture in straw bale walls. As a result of the study, the potential for mold growth was found to vary by structure. Buildings utilizing rain screens were found to have lower interstitial relative humidity and a lower risk of mold growth.