RDH Building Science
    Building Science Corporation

This study investigated a set of hybrid walls that used a combination of exterior insulation, diagonal metal strapping, closed cell spray polyurethane foam, and cavity fill insulation. The hybrid wall systems were financially analysed for cost effectiveness, thermally modeled for whole wall R-values, hygrothermally modeled for moisture durability, and structurally tested to ASTM E72.

Results showed that the hybrid insulated wall systems can cost-effectively provide robust thermal, air, moisture, and water barrier systems in one assembly while also providing structure. The cost analysis using RSMeans CostWorks showed that the optimal hybrid wall has an incremental cost at $2.20/ft2 of enclosure wall when compared to a standard 2×6 wall with OSB. Thermal modeling using Therm5 showed the importance of insulation placement to effectively reduce energy loss. Hygrothermal modeling using WUFI showed that the proposed hybrid walls reduced condensation risk from air leakage in cold climates by between 95% and 100% compared to a standard 2×6 wall with OSB sheathing. The ASTM E72 structural testing showed that the ultimate racking strength of a diagonally strapped XPS sheathed wall is tripled with the addition of 1.5 in. (38mm) of closed cell spray polyurethane foam to each stud bay. When compared to a standard 2×6 advanced framed wall with OSB, the hybrid walls showed 50% higher ultimate strength with significantly less displacement.

Note: This paper was presented at the 14th Canadian Conference on Building Science and Technology. It is copyrighted by the authors and is published with permission.

RDH Building Science