Monitoring of Double Stud Wall Moisture ...

URL: http://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/monitoring-doublestud-wall-northeast.pdf

Double-stud walls insulated with cellulose or low-density spray foam can have R-values of 40 or higher. However, double stud walls have a higher risk of interior-sourced condensation moisture damage, when compared with high-R approaches using exterior insulating sheathing. Moisture conditions in double stud walls were monitored in Zone 5A (Massachusetts); three double stud assemblies were compared: 12" of ocSPF, 12" of cellulose, and 5-½" of ocSPF at the exterior of a double-stud wall (acting as a control wall). These assemblies were repeated on the north and south orientations. Under "normal" interior conditions (functioning ventilation system, wintertime RH 10-30%), ocSPF walls with latex paint showed low risk; all sheathing moisture contents remained below 20%. However, the 12" cellulose wall had moisture contents over 20% on the north side. Under high interior humidity loading (non-functional ventilation system, 40-50% interior RH), all test walls showed moisture contents and sheathing-insulation interface RHs well into the high risk range. The cellulose walls showed particularly high moisture contents (sheathing over 30%), while the ocSPF walls showed MCs in the 18-25% range. In addition, the monitoring showed evidence of liquid water condensation in all walls (both north and south sides). During each summer after a winter of wetting, moisture levels fell well into the safe range. When the walls were disassembled at the conclusion of the experiment, the sheathing and framing showed remarkably little evidence of wetting damage or mold growth. No visible mold growth was found, nor evidence of staining or water rundown.

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Last updated May 6, 2016
Created May 6, 2016
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