Every material has a greater or lesser ability to allow water vapor to diffuse through to the drier side. This ability can be specified as either the material’s permeability or its permeance. Both tell how easily water vapor moves through a material, with higher numbers indicating more movement. The difference is that permeability doesn’t depend on thickness and permanence does. The former is an intrinsic property while the latter is extrinsic. The common term used in building construction is the “perm rating”, short for permeance, which means that it already factors in the thickness of the material, whereas permeability is dependent upon thickness.
In cold climates, vapor generated by indoor activities tends to migrate outward through exterior walls. As it does, it encounters colder air and may condense. A vapor retarder installed on the inside of the insulation prevents that movement and therefore the condensation. In hot climates, on the other hand, humid outdoor air migrating inward through a wall assembly can encounter a surface cooled by air-conditioning, and condense. The proper design of wall assemblies is dependent upon the climate and construction.
International Energy Conservation Code (IECC) and the International Residential Code (IRC) 2007 segment perm ratings into I, II or III perm rating classes. Our ENRG Blanket products can be manufactured as a class I, II or III perm rating, based on the procedures of ASTM E96 (Method B) Water Vapor Transmission Rate Testing.
We make ENRG Blanket to fit within each perm rating class so that architects have all options at their disposal. In climates where it is useful to use our vapor barrier or vapor retarder ENRG Blanket provides an additional benefit of a contiguous air barrier. Generally we recommend that Class 1 vapor barriers only be used with unfaced fibrous insulation; insulation that will allow the surface to dry to the exterior.
ENRG Blanket permeance options:
- Class I Vapor Barrier- Perm Rating <0.1 (Class A or Class C fire rating)
- Class II Vapor Retarder- Perm Rating = 1 (Class C fire rating only)
- Class III Permeable- Perm Rating >1 (Class C fire rating only)
Class I & II also function as an air barrier.
The image to the right is of our ENRG Blanket M51/Q25/Class C fire rating/Class III/>1 perm rating.
Below is information from the independent testing completed to determine perforation size for our vapor retarder and permeable options.
Moisture Driven Mold & Air Quality Testing
We acquired the services of a third party testing lab to validate the air quality inside of our testing site with our impermeable Class I Vapor Barrier ENRG Blanket product installed in the walls and ceilings. The test results show the comparison between a structure with Phase Change Materials installed within the walls and ceilings to one without. Testing, to measure the actual mold / air quality results, was performed using procedures following Allergenco Cassette Analysis of Fungal Spores & Other Airborne Particulates by Optical Microscopy (EMSL Method M001).
The full independent testing report is available, just contact us and we can send you a copy.