Confused About Perm Ratings? Try our New Perm Calculator!


W. R. MEADOWS is proud to announce that it has developed a new Perm Calculator which allows you to compare the amount of moisture that is transmitted through a vapor barrier. The materials of varying permeances are compared to the requirements listed in ASTM E1745 of 0.1 perms. The compared materials include Perminator 10 mil, Perminator 15 mil, and Comparable Material (click on “Show all W. R. MEADOWS products” to compare PMPC and PRECON as well).

Try our New Perm Calculator:

The calculator is designed to show the estimated amount of moisture that is transmitted through a material of a given permeance over a user defined area and time period.

For the sake of comparison, the pressure differential had been set as a constant at 0.106 psi. [Calculated using a slab exposed to a 70° F (21° C) and 30% relative humidity (RH) environment at the top and 55° F (12.7° C) and 100% RH at the bottom.]

Perm Calculator Instructions:

a) Enter the perm rating of the vapor barrier/retarder to compare.
b) Enter the floor area in square feet for analysis (for example: 1000).
c) Enter the time frame in hours for comparison (for example: 24 for one full day).

Enter the material you would like to compare to the W. R. Meadows products, floor area in question, and the desired time frame to obtain the transmitted water volume through a material of a given perm rating.


Perm Calculator Screenshot (click image to test calculator)

The resultant calculation will be the amount for water vapor that is transmitted through a given material of your choice in a variety of units for your comparison. The result will also be compared to the 0.1 perm requirement as defined in ASTM E1745. If you would like to compare the result to the materials with the industry’s lowest perm ratings for critical applications, select “Show all W. R. MEADOWS products.”

Try our New Perm Calculator:


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