Investigation of the proposed solar-driven moisture phenomenon in asphalt shingle roofs
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
We report that unvented, sealed or conditioned attics are an energy efficiency measure to reduce the thermal load of the home and decrease the space conditioning energy consumption. This retrofit is usually done by using spray polyurethane foam underneath the roof sheathing and on the gables and soffits of an attic to provide a thermal and air barrier. Unvented attics perform well from this perspective but from a moisture perspective sometimes the unvented attic homes have high interior humidity or moisture damage to the roof. As homes become more air tight and energy efficient, an understanding of the hygrothermal dynamics of the home become more important. One proposed reason for high unvented attic humidity has been that moisture can come through the asphalt shingle roof system and increase the moisture content of the roof sheathing and attic air. This has been called solar driven moisture. Oak Ridge National Laboratory (ORNL) investigated this proposed phenomenon by examining the physical properties of a roof and the physics required for the phenomenon. Results showed that there are not favorable conditions for solar driven moisture to occur. ORNL also conducted an experimental study on an unvented attic home and compared the humidity below the roof sheathing before and after a vapor impermeable underlayment was installed. There was no statistically significant difference in absolute humidity before and after the vapor barrier was installed. Finally, the outcome of the theoretical and experimental study both suggest that solar driven moisture does not occur in any significant amount.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE)
- Grant/Contract Number:
- AC05-00OR22725
- OSTI ID:
- 1260070
- Journal Information:
- Journal of Building Physics, Journal Name: Journal of Building Physics; ISSN 1744-2591
- Publisher:
- SAGECopyright Statement
- Country of Publication:
- United States
- Language:
- English
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