What’s Hot: Structural Insulated Sheathing

An interesting new product we have used recently is “Structural Insulated Sheathing” or SIS, a product of Dow. This is a structural sheathing product that includes an insulating layer bonded to the wood layer. It is installed like other sheet goods but provides an additional R value of 5.5 at a 1” thickness on the exterior of the wall to help eliminate thermal bridging of the insulation layer by framing components. When used with spray foam insulation, a very airtight wall system can be constructed. SIS is cost effective because it takes the place of other wall sheathing and when the seams are taped, additional house wrap, weather barrier, and drainage plane may be needed depending on type of siding used. Learn more here – a Building Science Primer written by Pat Huelman of the Cold Climate Housing Program at the University of Minnesota.

What’s Not: Moisture in Wall Cavities

This is a photograph of black mold that formed within a few days of sheathing being installed. The house was being remodeled and the heat and humidity from the living space was escaping into the garage where this picture was taken. Moisture was condensing on the cold sheathing material providing all of the three necessary conditions for mold to flourish; heat, water, and food. This condition was remedied before insulation was installed. Mold in wall cavities is a serious issue in cold climate construction where warm moist air is being driven into the wall cavity. Learn more about mold here.