Performance and Durability of Wall Assemblies using Mineral Wool Exterior Insulation in the Pacific Northwest

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As building codes become more stringent, the use of exterior insulation is becoming common practice in both commercial and residential building types alike. Using exterior insulation throughout the building enclosure is a design method that minimizes the effects of thermal bridging, increases the thermal performance of the enclosure, and reduces risk for potential condensation and moisture concerns. One of the more common insulation types to use for these applications includes rigid foam boards such as XPS or EPS. Concerns with using mineral wool insulation as exterior insulation, a vapor permeable semi-rigid insulation board, are common in the industry. In the Pacific Northwest, where rainfall is a steady factor, these concerns can highly influence the decisions made for building enclosures. Although there are studies that provide scientific evidence that mineral wool will not hold moisture, and will drain and dry with similar performance as that of rigid foam insulation, actual performance data will help ease these concerns. This paper looks at the in-situ performance of mineral wool insulation used in combination with a vapor permeable weather resistive barrier on the exterior side of the assembly in the Pacific Northwest, in a test hut application with intentional wetting cycles and a monitored building.