STP922

    Wetting of Polystyrene and Urethane Roof Insulations in the Laboratory and on a Protected Membrane Roof

    Published: Jan 1987


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    Abstract

    When subjected to a sustained temperature gradient in the presence of moisture in laboratory wetting tests, urethane and expanded polystyrene roof insulations accumulate enough moisture to reduce their insulating ability significantly. Extruded polystyrene is quite resistant to moisture in such tests. But the vapor drive is not as great in actual roofs, and it may reverse direction, thereby seasonally drying the insulation. To determine how well the laboratory tests could predict the wetting rate of insulation in actual protected membrane roofs, extruded and expanded polystyrene and urethane insulations were installed in a protected membrane roof in Hanover, New Hampshire. After three years of exposure, little moisture had accumulated in the extruded polystyrene, and it still retained essentially all of its initial insulating ability. Moisture progressively accumulated in 16-kg/m3 (1-lb/ft3) and 30-kg/m3 (1.9-lb/ft3) expanded polystyrene insulations, and at the end of the test they retained only about 30 and 40% of their initial thermal resistance, respectively. The urethane accumulated enough moisture to reduce its insulating ability to about 30% of its dry value. The laboratory tests provided a valuable indication of the potential long-term moisture gain of these insulations when installed in protected membrane roofs in cold regions.

    Keywords:

    roofs, protected membranes, thermal insulation, cellular plastics, urethane, styrene, moisture, wetting, thermal conductivity, thermal resistance


    Author Information:

    Tobiasson, W
    Research civil engineer, and civil engineering technicians, U.S. Army Corps of Engineers, Hanover, NH

    Greatorex, A
    Research civil engineer, and civil engineering technicians, U.S. Army Corps of Engineers, Hanover, NH

    Van Pelt, D
    Research civil engineer, and civil engineering technicians, U.S. Army Corps of Engineers, Hanover, NH


    Paper ID: STP18495S

    Committee/Subcommittee: C16.22

    DOI: 10.1520/STP18495S


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