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    Effect of Moisture on Thermal Resistance of Some Insulations in a Flat Roof under Field-Type Conditions

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    Specimens of glass fiber, phenolic foam, and extruded polystyrene foam insulation with moisture contents ranging up to about 25 percent by volume were mounted in the roof of an experimental building. The interior of the building was maintained at about 21°C and normal weather conditions prevailed outside.

    Thermocouples were located at the upper and lower surface of each insulation specimen and at the quarter points of some specimens. A calibrated heat flow meter was used to measure heat flow through each specimen continuously for a period ranging from about 7½ to 18 months for wet specimens and somewhat less for some of the dry ones.

    Heat flow rates were plotted against temperature difference using daily arithmetic averages in most cases; two-week averages were used in a few cases. For open-cell and fibrous insulations of 20 percent moisture content, heat flow rates exceeded rates for dry insulation by a factor of two or more. The data points were scattered. Inspection suggested that this was partly owing to moisture distribution, which affected the rate of heat flow at a given temperature difference.

    Measurements at the quarter points provided information about temperature gradients along the path of heat flow, and hence about moisture distribution in the insulation. These results suggested that moisture migrated to the upper layers in the wintertime, leaving the lower layers nearly dry.

    Ratios of heat flow in wet and dry specimens were in fairly good agreement with those obtained by other investigators.


    moisture, moisture migration, thermal resistance, open-cell insulation, closed-cell insulation, wet insulation, heat flow, heat flow meters, roof insulation

    Author Information:

    Hedlin, CP
    Research Officer, Prairie Regional Station, Division of Building Research, National Research Council of Canada, Saskatoon, Sask.

    Committee/Subcommittee: C16.30

    DOI: 10.1520/STP29474S