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    Measurement of Effect of Moisture on Heat Transfer Through Insulated Flat-Roof Constructions

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    Two methods are described for the laboratory determination of the effect of moisture on the heat transfer through insulated flat-roof constructions subjected to successive periods of simulated summer and winter temperature conditions with daily solar heating of the top surface. The methods allow determinations of changes in the insulating value of the entire construction and also of its components due to moisture to be made simultaneously on specimens of different designs. The first method employs heat-flow meters, the second method a calorimetric technique; the second method also includes a means for measuring the rate of change of the moisture content of the specimens. Illustrative results are given for 13 of the 54 specimens tested over a period of 5 yr. Results indicate that natural in-place drying of wetted insulation over a vapor barrier or over a dense concrete deck is very slow and that, once wetted in such installations, insulation will have a greater than normal heat transmission for long periods of time. Some constructions made without vapor barriers, containing materials of moderate permeance, showed good drying characteristics, so that if initially wet, or wetted later, the insulation approached dryness in a period comparable to a year's service.

    Author Information:

    Powell, F. J.
    National Bureau of Standards, Washington, D. C.,

    Robinson, H. E.
    National Bureau of Standards, Washington, D. C.,

    Committee/Subcommittee: E06.22

    DOI: 10.1520/STP45800S