Exposure to Condensation Moisture of Sheathing in Retrofitted Leaky Wall Assemblies

Exfiltration of moist indoor air during winter conditions may lead to the gradual wetting of the sheathing of wall assemblies that are not airtight. In this study, seven full-scale wood-frame wall specimens were tested to evaluate the impact of both the geometry of the air leakage path and the addition of rigid insulation on the warm side or the cold side of the assembly on the hygrothermal response of wall assemblies. Walls were exposed to $72\text{days}$ of steady-state winter conditions and $47\text{days}$ of steady-state late spring conditions. The position of the added rigid insulation and the geometry of the air leakage paths were different in each wall specimen. The moisture content of the fiberboard sheathing was monitored, and the results are presented. The evolution over time of the moisture distribution across the plane of the sheathing is also presented. The duration of exposure to moisture content above 19 and 28% is examined, allowing a comparison of the performance of the specimens. Leaky assemblies with vapor-tight insulation board added on their cold side were exposed to high moisture content longer than the assemblies not reinsulated or reinsulated on their warm side because the assemblies without insulation on the cold side of the sheathing were exposed to a buildup of frost that prevented moisture to be absorbed by the sheathing.