What perm rating should an air barrier have?
Air barriers are often confused with vapor retarders. Perm ratings are attributed to vapor retarders, not air barriers. An air barrier may or may not be vapor permeable. An air barrier’s performance is measured in air leakage, not perms. Air leakage units are typically given in CFM/ft2 or L/s*m2 at a given pressure differential. According to the Air Barrier Association of America (ABAA) an air barrier material must provide an air leakage rate of less than 0.02 L/s*m2 at 75 Pa pressure difference. CCW-705 self-adhering and Barriseal fluid-applied membrane air barriers meet this performance criterion when applied according Manufacturer’s instructions.
