Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Number 2 10/03 Paint and Gypsum Board Q. How do typical latex paints, with permeance in the range of 5 to 9 perms, impact MemBrain’s ability to allow systems to dry toward the interior? A. Latex-painted gypsum board, combined with MemBrain™ as an interior vapor retarder, will not impact the ability of the wall system to dry towards the interior during periods of high relative humidity in the insulated cavity. The amount of moisture allowed to diffuse through MemBrain under high relative humidity conditions is relatively small and manageable by the gypsum board. This buffering action, along with the permeance of paint, allows for system drying toward the interior. Vapor retarders are defined as having a water vapor permeance of 1 perm or less, when tested in accordance with the ASTM E 96 standard, dry cup method. Historical data from ASHRAE on water vapor permeance of typically applied latex paint is between 5 and 9 perms under dry conditions. Semi-permeable latex paints, as described above, are recommended without vapor retarders in warm-humid and mixed-humid cooling dominated climates to allow insulated wall cavity systems to dry toward the interior. The application is described in the ASHRAE Handbook of Fundamentals and the Energy & Environmental Building Association’s Builder’s Guide. Q. What is the permeance of gypsum board? A. The water vapor permeance of unpainted ½ inch gypsum board (drywall) varies between 20 perms, under very dry conditions, and 90 perms, under very wet conditions. Results will be similar for 5/8-inch thick drywall. The data is published in the 2001 ASTM Technical Publication MNL40, Moisture Analysis and Condensation Control in Building Envelopes. The permeance of 3/8 inch unpainted drywall, published in the ASHRAE Handbook of Fundamentals, is 50 perms.