We throw the term “perm rating” out quite a bit, but don’t always put it in context. A perm rating is a measure of moisture permeability, a scale that indicates how much moisture vapor can penetrate through a product.
When wood floors are installed, it is important to protect them from moisture vapor that can rise through foundations and sub-floors. This moisture can easily damage wood floors and cause warping or cupping. The National Wood Flooring Association (NWFA) has set guidelines for perm ratings between 0.7 and less than 10. We offer several options that are tested by an outside lab that meet these requirements:
- Aquabar “B” : the industry leading underlayment that consistently achieves a perm rating less than 1 (0.87 actually).
- HWD-15: an asphalt saturated vapor retarder with a perm rating of less than 5.0.
Always be sure to check the manufacturer’s data sheet for published perm rating. Also, note that products designed for vertical walls, including many black asphalt saturated kraft products, are not intended as vapor retarders for floors. These products may have a higher than acceptable perm rating, leaving a flooring install subject to moisture damage. These wall products do NOT meet industry standards for floors.