NRDCA Educational Conference and Association Meeting

High humidity and corrosive indoor environments pose special risks and challenges due to moisture condensation in roofs. Perforated metal decks with acoustical insulations are commonly used as roofs that serve as acoustical absorbers. In some applications, non-perforated metal decks are used as well. Without the existence of standards for roof design, based on a simple, steady-state dew-point analysis, the common practice is to employ at least a 0.1 perm vapor retarder on the warm side of the assembly to eliminate the risk of condensation presumably. Nevertheless, rust and corrosion of the metal roofs are a common occurrence. The use of the vapor retarder in such roof assemblies in preventing condensation is not well understood. This study investigates the role of a vapor retarder in a roof assembly by hygrothermal modelling in Climate Zones 2, 7 & 8 using a well-known hygrothermal simulation model (WUFI). An alternate wood composite roof deck that provides acoustics, thermal insulation, and a nailable surface such as oriented stranded board (OSB), with and without a vapor retarder, at different locations in the assembly is used as a roofing candidate for the simulation. The moisture accumulation in the OSB board over the years of exposure is used as an indicator of the roof’s performance. In addition, the presence of a dew point to verify the occurrence of condensation in the assembly is monitored.

Heat and moisture transport in typical roof deck assembly made from Light Weight Concrete and EPS insulation is also presented. In particular, the temperature of the roofing membrane of a Lightweight Concrete roof deck is compared to that of a roofing deck that is insulated with Polyisocyanurate foam over a 10-year period.