Moister Barrier
15# or 30# Felt ~ Felt paper is most commonly used as a moister barrier between sheetrock and brick or siding on a home or business. In roofing, felt paper is used to keep the chemicals sprayed on plywood off the backside of the laminated shingles. The 15# felt is the preferred weight of all major manufacturers because it absorbs less condensation allowing the shingles to last longer. The 30# felt is mostly used on very steep roofs to help installers get a better grip to walk on and 30# felt is also mandatory in hurricane zones.  
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