Abstract

Installing roofs with high solar reflectance and high thermal emittance, known as “Cool roofs”, are becoming popular because of their cooling energy saving potentials, cost effectiveness and sustainability. Cool roofs may affect the hygrothermal performance of roofing systems and hence their performance should be characterized in different climates.
We simulated the performance of several roofing systems including: Typical, smart, and self-drying roofs for residential and commercial buildings. In addition, we proposed vented roofs with smart vapor retarders in different climate regions across North America. We also developed an algorithm to investigate the effect of snow on hygrothermal behaviour of black and white roofs.
Results showed that office buildings never experience moisture accumulation problem in the simulation period (5 years). In residential buildings, white typical roofing compositions with conventional vapor retarders experienced moisture accumulation problems in cities such as Anchorage, Edmonton and St. John’s. Using smart vapor retarder (smart roofs) or self-drying roofs helped to decrease risk of moisture accumulation. We showed that in these climates, adding a ventilated air space along with using smart vapor retarder eliminated risk of moisture accumulation and prevented excessive OSB (oriented strand board) moisture content. Furthermore, our simulation results showed that risk of mold growth was significantly lower in vented smart roofs than other systems. Simulating the effect of snow on the roof for Anchorage, Montreal and Chicago showed that the hygrothermal performances of white roofs improved with snow accumulation on the roof.