Comparing one sheathing wrap to another is difficult since there is no single test standard for all products, and even where manufacturers follow the same standard, test conditions may vary dramatically from one company to the next.
More important may be the material’s ease of installation and durability over time.
In general, a sheathing wrap should have a permeance of at least 5 perms, similar to dry asphalt felt.
High permeance allows wall assemblies to dry out should they get wet.
In comparing sheathing wraps (also called sheathing paper and housewrap), you can look at a lot of technical specs regarding permeance, water resistance, and air infiltration.
Unfortunately, these tests don’t tell us too much about real world performance.
This indicates how quickly water can dry out if blocked by this material.(Technically speaking, one perm = one grain of water vapor passing through 1 square foot per hour per inch difference in vapor-pressure).
Queda prohibida la reproducción, distribución, comunicación pública y utilización, total o parcial, de los contenidos de esta web, en cualquier forma o modalidad, sin previa, expresa y escrita autorización, incluyendo, en particular, su mera reproducción y/o puesta a disposición como resúmenes, reseñas o revistas de prensa con fines comerciales o directa o indirectamente lucrativos, a la que se manifiesta oposición expresa.
Another advantage of traditional asphalt felt is that it can absorb excess moisture and release it later when drying condition improve.
In order to be accepted by code as a “water-resistive barrier,” a housewrap must meet specific measures for permeance to water vapor, resistance to liquid water, and air infiltration. Permeance ratings measure the rate at which water vapor (as opposed to liquid water) passes through a material.
Some of the synthetic products look great on the day of installation, but degrade quickly when subjected to prolonged wetting or exposure to UV. asphalt felt often outlasts the synthetic housewraps, especially where it remains wet for extended periods.
Under prolonged wetting, plastic housewrap tends to deteriorate.