On every roof replacement that we install nowadays, we use a synthetic felt instead of the older tar paper. You can see in the picture on the right, we removed a 3-tab shingle and the old black tar paper started to dry out and deteriorate from the extreme heat, causing the brown lines to form in between the seams of the shingle tabs. On the left is a synthetic felt that can last for 50 years under shingles before it will start to deteriorate. It’s kind of like a Ledo pizza. We don’t cut corners when it comes to your roof.