I fixed my roof a few years ago, and have part of a roll of tar paper sitting in the basement. I’m now re-laying some hardwood flooring. Can I use that leftover stuff as underlayment, or is there some subtle but important difference between “flooring” tar paper and “roofing” tar paper that means I ought to go buy some other product?
(If it matters, the house was built in the 1940s and uses materials typical of that era. I’m just doing repairs/small modifications, so I’m patching in like-for-like stuff.)
I just read into it a little bit. Seems that I was wrong, and “tar paper” is typically not completely waterproof, it’s just water resistant. Most stuff these days isn’t technically tar paper, either, it’s roofing felt. I guess it’s only called paper if it’s made from cellulose. Apparently they did make the felt from asbestos back in the day.
Seems like it’s definitely common enough to use it under flooring, especially if it’s a thinner grade.