What felt paper does
What purpose does felt paper serve when applied to a roof that will be shingled?
Chris Dillon, Rocky Point, NY
Larry Haun, author of The Very Efficient Carpenter, replies: I was told that felt paper helps prevent leaks and that two layers on a roof are better than one. Under some types of shingles, wood shakes for example, the paper is the basic sealant.
Shinglers tell me that putting felt paper under composition shingles extends the life of the shingles. Wood sheathing and composition shingles expand and contract at different rates as the temperature rises and falls. The paper between acts as an expansion joint.