We recently purchased a lake house and found moldy framing and drywall. The removed drywall had a black backing on it, similar to felt paper. This part of the wall is sub-grade with wood (gc 2x6’s) behind the drywall. It’s a split-level pier and beam house. I would like to replace the drywall with OSB or something more water tolerant, but am wondering if roofing paper would be appropriate behind it.

  • I have not seen drywall with a black backing Could it be tar paper or felt that is stuck to the drywall. I would use water resistant Sheetrock before OSB for fire rating and the ability to finish without a large expense. What is the exterior siding and is there a vapor barrier? – Ed Beal May 22 at 15:27
  • I found a small strip attached to the Sheetrock while cleaning earlier.. it says “water resistant Sheetrock.” Also, I (yesterday) had a foundation crew out and they put 20ml plastic sheeting on the exterior side of the exposed boards. But, this is all in the crawl space under the bedroom floors. So this hall is 1/2 below grade and 1/2 above. Understand the concern re: fire ratings, will go back th Sheetrock. – Peter Schmidt May 22 at 16:13

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