Moisture transport in ventilated attic spaces for hot-humid climates

Ventilated spaces in the built environment create unique and beneficial microclimates. While the current trends in building physics suggest sealing attics and crawlspaces, comprehensive research still supports the benefits of the ventilated microclimate. Data collected at the University of Florida Energy Park show the attic environment of asphalt shingled roofs to be typically hotter than the outdoor conditions, but when properly ventilated, sustains a much lower relative humidity. The hot, humid regions of the United States can utilize this internally convective air mass to provide stable moisture levels within attic spaces. Positioning the buildings primary boundary at the ceiling deck allows for utilization of a buffer climate to minimize moisture trapping in insulation and maximize the insulation's thermal benefits. This investigation concludes that the conditions in a ventilated attic are stable through seasonal changes and promote cost effective, energy efficient climate control of unconditioned spaces in hot, humid regions.;Hot and humid climates present a challenge to limit moisture entrainment and condensation within the building envelope. Ventilated attics perform the function of purging intruding moisture. Ventilated attics change with the seasons to make the best 11 use of ceiling insulation and maintain building health. Soffit and ridge vent configurations suppress excessive ventilation during mornings hours limiting the dense, moist air coming in contact with a cool duct surface.;Using computer simulation and a mathematical model, the data collected at the University of Florida Energy Park was used to investigate the interaction of mechanical ventilation ductwork placed in residential attics. Output data from this model show moisture can condense at the duct surface under certain conditions. Proper installation reduces the duct leakage and mitigates the effects of condensation. Thus the data indicate crimped or damaged ductwork can sufficiently cool the surface to lead to condensation.