Excessive moisture in CMU, concrete, exterior gypsum sheathing and wood based sheathings can cause premature damage and adversely affect the long-term performance of the building envelope.
Installers and applicators of air and vapor barriers are regularly asked to apply products over questionable substrates and regularly ask air and vapor barrier manufacturers about acceptable moisture content levels within the substrate in which the barrier will be applied. To this end the following guidelines should be followed:
Wood based sheathings (plywood, OSB) shall be at a moisture content of 19-percent or less. Some experts require a moisture content of 16-percent or less.
Exterior gypsum sheathing shall be at a moisture content of 1-percent or less.
Accepted ranges for concrete and CMU are not specifically provided and specifications typically only require that the surface be dry. A good rule of thumb, however for concrete and CMU is a moisture content of less than 5-percent for fluid applied air and vapor barriers and 12-percent or less for self-adhered air and vapor barrier membranes.
The design professional and substrate manufacturer should always be consulted for establishing the level of acceptable moisture content in the substrate. Further, relevant ASTM standards should be reviewed to verify the criteria are at appropriate levels for in-service performance.
Contact the air and vapor barrier experts at Carlisle Coatings & Waterproofing for project specific questions, details and applications guidance. They may be reached at 888-229-2199 or email@example.com .
For straight-forward information about how new wall assemblies containing plastic foam insulation and combustible weather barriers can meet tough new NFPA 285 standards, please visit fireresistccw.com.