INFRARED TECHNIQUE AS A RESEARCH TOOL FOR MEASURING WATER-VAPOR TRANSMISSION OF ROOFING MEMBRANES

Measurements of the permeability to water vapor of materials intended to prevent its transmission are time-consuming with the usual cup meth od [1]. Several instruments have been promoted as being capable of pro viding results rapidly, but doubts about their agreement with cup meas urements have delayed their use for more than quality control. One ins trument with an infrared sensor was studied to investigate its accurac y and to correlate results obtained with the standard cup methods. Fac tors studied include those that contribute to the inconsistent perform ance of the instrument, especially for research work. Techniques for i mproving the precision and the accuracy of the instrument are discusse d. The permeances of roofing papers and felts and of plastic films by both the modified IR instrument and the cup methods are reported and c ompared to values given in the literature.