Field Monitoring of Cold Climate Double Stud Walls with Cellulose and Low-Density Foam Insulation

Double-stud walls insulated with cellulose or low-density spray foam can have high R-values; compared to approaches using exterior insulating sheathing, double-stud walls are typically less expensive, and have exterior details similar to typical construction. However, double stud walls have higher risks of interior-sourced wintertime condensation damage. Field monitoring was installed in a Zone 5A climate house with 12” thick double stud walls; assemblies included 12” open cell polyurethane spray foam, 12” netted and blown cellulose, and 5-½” open cell spray foam at the exterior of the stud bay.

Data were collected for three winters. ASHRAE 160 criteria were applied to the monitored data; all walls failed (i.e., mold growth likely). However, 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. The damage was limited to some grain raise of the interior surface of the OSB at the cellulose wall, and corrosion of fasteners.

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