Hygric Redistribution in Insulated Assemblies: Retrofitting Residential Envelopes Without Creating Moisture Issues

The Building America program has recognized that most of the current housing stock is in need of energy related retrofits. One of the best ways of reducing the space conditioning energy consumption is to improve the thermal performance of the enclosure by adding exterior board foam insulation. This report quantifies the amount of water that can become trapped in the drainage cavity of typicalwall systems, and measures the effect of water trapped in the drainage cavity on the moisture content of the sheathing. This study also attempts to explain the discrepancy between hygrothermal simulations and field performance of low permeance, low R-value exterior insulation (e.g. 3/4-in. foil faced polyisocyanurate) in cold climates.