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Open Access Publications from the University of California

Measured Thermal and Moisture Performance of an Air Sealed and Insulated Attic with Porous Insulation

  • Author(s): Less, B
  • Walker, I
  • Slack, J
  • Levinson, R
  • et al.

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Sealed and insulated attic construction can provide substantial HVAC energy savings in homes with space conditioning equipment in the attic. But these assemblies also come with moisture risks, largely due to condensation on cold sheathing surfaces, combined with no mechanism for subsequent moisture removal. Spray polyurethane foam has traditionally been used as both a sealant and insulation material, while also reducing moisture risk. As part of an effort to drastically lower the cost of this construction method, we have instrumented two occupied, test homes in the Fresno region of California’s Central Valley that have sealed and insulated attics using solely unfaced R38 fiberglass batt insulation. Our goals are to assess if the attics can be considered to be within conditioned space, and if moisture problems are apparent using this low-cost building strategy. We found that the sealed and insulated attic can be considered as conditioned space, due to the tight coupling of the occupied and attic zone air temperatures. We also found some evidence of moisture risk at the North ridge sheathing. Condensation was present for substantial periods of time, which was also associated with increased wood moisture content up to 25.9%. The monitored assembly is currently within the moisture acceptability criteria established in ASHRAE Standard 160, but it is not clear whether it will continue to be safe or fail in future winter seasons. Ongoing field observations and hygrothermal simulations will be used to more fully assess the long-term moisture risks throughout California

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