Abstract
This paper describes a simplified analysis of the heat and moisture re sponse of protected membrane roofs. The evaluation includes the ΔU correction to the thermal transmission coefficient U 0 representing the effect of moisture accu mulated in the insulation boards. This ΔU correction is affected by four different mechanisms: percolation of rainwater under the insulation, evaporation of the pond ing water and its flow through the insulation, an increase in thermal conductivity of the insulation caused by the presence of moisture in the boards and the effects of thermal bridge created by the joints between the insulation boards. The risk for moisture accumulation in the boards is associated with the presence of ponding water below and the ability of insulation to retain some of the moisture permeating through the boards.
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