30-lb Felt Underlayment UV Exposure?


How long can 30-lb felt underlayment be exposed to sun before new 30-lb felt underlayment is required? Can anyone provide reference material? Thanks for your help.

If you are referring to asphalt-saturated felt about 2-1/2 to 3 months.
But does anyone use that anymore?

Until the first rain and then when the sun hits it, it will wrinkle so bad that it would telegraph right through the roof shingles.
Better to not use it at all if it stays exposed. Like Roy said, why use it at all when there are synthetic underlayments that are so much better. :smiley:

If it gets wet, just wait a few hours in the sun. It will shrink right back to flat. Personally, I would have it covered within a few days, but I think it will be ok for up to a month or so if it doesn’t blow off first.

Up in colder country and time of year, ripples caused by rain stay rippled. Not enough heat to lay flat.
So depending where you are, I would recommend to cover it as soon as you can.

Yes, I remember those days. We’d roll it out as we shingled or get what Marcel’s picture shows.

P.S. That out be an old picture, Marcel,…no Grace Ice and Water at the eaves and so forth.

Check the manufacturer installation requirements.

Closest thing I could find on line Larry to resemble what memory brought back. :wink:


If the felt has buckled or greatly faded I would not shingle over it.

I never saw ripples in felt after a rain. Sometimes we could not work for several days due to a low front. Truly, I cannot recall on 1 project I was on and I was a roofer.

Personally, I was fastidious laying out the felt and fastening the ply to the sheathing. It all starts the starter course. I wanted lines for course correction.
Poorly fastened membrane, you could end up sliding of the roof on the felt. Keep the roll tight to the sheathing.

IKO had the crew chalking many times due to manafuring length imperfections. They were told to leave Quebec. The company moved across the border into Ontario.
Anywho, that my take on rippled felt.