Abstract

Rainwater entry and penetration through a waterproofing layer, such as external finishing and sheathing membrane, should be avoided to prevent moisture damage to a wooden wall assembly. However, housing warranty insurance organizations in Japan have reported that deterioration in some wall assemblies was caused by rain penetration, and severely damaged walls were detected in airtight and insulated building envelopes. This paper presents various factors of water entry and penetration of the waterproofing layers in wooden wall assemblies in terms of practical situations, as a part of a research project to reveal the risk of water and moisture accumulation in collaboration with government and industries in Japan. Several experimental works using mock-up specimens replicating a part of the wall assembly were carried out. As for external finishing, the water intrusion was observed not only at the joints but also at the bottom of vented cavities. Although these minor defects must be prevented by proper design and site work, it is difficult to avoid them completely through the construction process and period of use. Indeed, the extent of water entry was affected by various factors such as wall configuration, exposure conditions and so on. Experimental results suggested that various factors, including detail of interface and quality of materials, should be considered to assess service life prediction by hygrothermal analysis.