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June 5, 2012
Hot Dry Mixed Dry
This report summarizes hygrothermal analysis of specific attics constructed in California. The analysis was done using historical experience, published work in journals and trade publications, current building code requirements and WUFI hygrothermal simulations to assess benefits and risks associated with insulating the roof decks in both vented and unvented configurations. The majority of the configurations evaluated are well understood and have been addressed in previous published work or in the model building codes. However, the focus of this report is on modifying conventional, ventilated attics, constructed with impermeable roof shingles (with fiberglass batt insulation on the ceiling plane) by adding fiberglass batt (or netted fiberglass or netted cellulose or spray applied fiberglass) insulation to the underside of the roof deck (i.e. on the slope) while leaving the attic air space ventilated to outdoors.
RR-9701: Measurement of Attic Temperatures and Cooling Energy Use in Vented and Sealed Attics in Las Vegas, Nevada