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Association for their thorough reviews and constructive comments. We also wish to thank Jeffrey E. Christian for continuing support of our activities in this area. Finally, thanks to LeRoy GiUiam, who produced most of the graphics for this report, and to Deborah Counee and Carolyn Moser, who edited the report and readied it for publication. xi ABSTRAC_ Issues associated with removing excessive moisture from low-slope roofs have been assessed. The economic costs associated with moisture trapped in existing roofs have been estimated. Based on the limited amount of _vailable data, the evidence suggests that existing moisture levels cause approximately a 40% overall reduction in the R-value of installed roofing insulation in the United States. Excess operating costs are further increased by a summertime heat transfer mode unique to wet insulation, caused by the daily migration of water within the roof. By itself, this effect can increase peak electrical demand for air conditioning by roughly 15 W/m2 of roofing, depending on the type of insulation. This effect will increase peak demand capacity required of utilities in any geographic region (e.g., 900 MW in the South). A simple formula has been derived for predicting the effect that self-drying roofs can have upon time-averaged construction costs. It is presumed that time-averaged costs depend predominantly upon (1) actual service life and (2) the likelihood that the less expensive recover membranes can be installed safely over old roofs. For example, an increase in service life from 15 to 20 years should reduce the current cost of roofing ($12 billion/year) by 21%. Another simple formula for predicting the reroofing waste volume indicates that an increase in service life from 15 to 20 years might reduce the current estimated 0.4 billion ft3/year of waste by 25%.