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The effect of moisture on the thermal cConductance of roofing sytems

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Abstract
The results of laboratory tests are presented describing the effects of the moisture content on the thermal conductance of roof systems containing insulation. Roof systems, consisting of five types of rigid board roof insulations with attached four-ply bituminous built-up membrane, were tested. Moisture was induced into the roof system specimens by maintaining a constant water-vapor pressure difference across them. Moisture gain in the insulation varied depending on the type and thickness of the insulation. A procedure was developed using a heat-flow meter apparatus to carry out thermal conductance tests on roofing specimens containing moisture. More than 200 tests were performed over a wide range of moisture contents. The approximate moisture distributuion in the insulation was determined from core samples. Relationships between the thermal conductance and moisture content are presented. The relationships show that the presence of moisture in roof systems can cause significant increases in thermal conductance, depending on the type and thickness of the insulation.
Date
4/1980
Author(s)
Lawrence Knab ; Robert Mathey; David Jenkins
Page(s)
45
Keyword(s)
built up roofing; insulation; moisture; thermal conductance; thermal resistance; thermal conductivity


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