September 16, 2013


Unvented roof strategies with open-cell and closed-cell spray polyurethane foam insulation sprayed to the underside of roof sheathing have been used since the mid-1990's to provide durable and efficient building enclosures. There have been isolated moisture related incidents that raise potential concerns about the overall hygrothermal performance of these systems. This project involved hygrothermal modeling of a range of rainwater leakage and field evaluations of in-service residential roofs using spray foam insulation. The exploration involved taking a sample of spray foam from the underside of the roof sheathing, exposing the sheathing, then taking a moisture content reading. All locations had moisture contents well within the safe range for wood-based sheathing.