Hey all. New to the site.   I'm curious about roofing felt. I use 30#, recycled content for exterior walls under a rain screen as well as the same 30# under steel for the roof.  Does anyone have info on the life expectancy of felt? 

I focus on old structures and see thin but serviceable felt that's over a hundred years old in some walls but a recent advertisement for a new roof underlayment claims felt only lasts 30 years.  

As a green builder I choose products using a matrix of life expectancy/durability, embodied energy, recyclability and so on, and I've always chosen recycled felt as the best material.  So two questions, if I may:

1. Am I wrong to listen to what is probably green washing for a new product?

2. Am I just plain wrong about felt?

Thanks for any help!

Michael McAuley
McAuley Building Conservation
Bellingham, WA