Also published in RCI Interface, April 2014
Abstract: In recent years, the roofing industry has become increasingly aware of the problems caused by moisture in concrete roof decks that migrates into the roofing system. Installing a vapor retarder over the concrete deck is the primary method of addressing this problem. This paper summarizes some of the challenges associated with incorporating a vapor retarder into the roofing system. For example, selecting a vapor retarder of the appropriate vapor resistance is challenging due to the shortage of published data on the acceptable moisture limits of roofing materials. We explore the question of acceptable moisture limits through an extensive review of published literature, product-specific recommendations from manufacturers, and some preliminary laboratory testing of some common roof cover boards. This paper is based on the authors' experience as designers and investigators of roofing systems, literature review, and laboratory testing.