Another Synthetic Underlayment Question

shopman

I have read the previous posts about synthetic underlayments, and see alot of people dont use them because they have not been proven and are a fairly new product. I am curious have they ever done a study of two identical roofs, same amount of ventilation, same weather conditions, etcc. And made one roof with 30# felt and the other with synthetic underlayment? I would be curious what affect synthetic underlayments have on the life of a shingle. Do you think shingles would last longer using synthetic verses organic felt?

I would hate to have synthetic underlayment and find out 5 years down the road that the stuff has some adverse affect on the shingles and makes them fail prematurely.

red_cedar

I am sure that somewhere there has been a study comparing the 2 underlayments, but not sure about some accelerated type weathering test .

I use and have been useing some of the synthetics for several years. Overall, they are a much better product then the asphalt based felt papers. However, with the synthetics, proper ventilation plays a much bigger role, due to the fact that they do not breath. Where the regular felt papers do allow some moisture laden air to pass thru.

I believe we will see problems, premature shingle failures, useing the synthetics. We see shingle failures now with regular felt paper.
Not because of the product, but because of not being vented correctly.

jmorgan

Actually, these synthetic felts have been used in Europe for 15+ years. These jobs are mostly tile. Not enough "breathing" takes place through felt to make much difference. Most of the "breathing" takes place at the overlaps. Because of the widths of synthetics, there are less laps, so less "breathing". Most synthetics are made of propylene, which does not react with asphalt. I think they are the wave of the future.
Jim

Happy

I don't get the issue of synthetics breathing less than felts for a shingle roof? GAF has a breathable underlay on the market for shingle roofs, but I don't get how it can work? Even if the moisture from the deck can permeate through the synthetic breathable underlay, who can it escape into the air if you have shingles on top?

jmorgan

They breath like Gor-Tex clothing. Personaly, I don't see the issue.....if the deck is vented as required by code (1:300). I have put many hot and singleply membranes on 2:12 slopes with no problem. These materials are true vapor barriers and don't let any moisture through. I double checked venting on all of these jobs. The synthetics have 20-30 year warranties and are great to work with.
Jim

joasis

I don't have a problem with synthetic underlayments like Tri-Flex, which we have used. However, they are treacherous to walk on with any higher pitch roof....anything over 6/12 is a killer.

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RooferJim

Tried them, guys thought they were crap and went right back to felt.
if it ait broke dont reinvent the wheel

RooferJim
www.jbennetteroofing.com

jmorgan

RooferJim,
Which ones did your guys try? What didn't they like?
Jim