Breathable Synthetic Underlayment

John Nguyen
5/10/2011
I'm in the process of getting a standing seam roof put on my house. However, I can't seem to make a decision on the underlayment to use. After much reading on the net, I keep running into opinions that breathable synthetic underlayment is necessary for metal roof. Are the benefits really worth the extra $. Is it even necessary in my location (Dallas, TX)? Can someone help? Thanks.
Todd Miller
Classic Products, Inc.
5/10/2011
If your home has "normal" construction including an attic with intake and exhaust vents, then I see no compelling reason for a breathable underlayment. However, in any event there should be some sort of underlayment product put in place before the new roof. Write back if you do not have attic ventilation or if you have been told some specific reason for the need for a breathable underlayment.
John Nguyen
5/10/2011
Thanks for the reply Todd. The home is a 1.5 story with an attic over the garage and an attic over the second floor. The attics have soffit/gable vent ventilation. My concern is the vaulted ceiling in the living area (in the pic - the area above the big windows). Can I assume that area is properly vented, possibly into the gable at the topmost ridge (in pic). No one has told me to use breathable underlayment for any specific reason. After much reading, I just figured it was the safest route. I was initially set on just a synthetic underlayment like Palisade til I started doing more research. Is this overkill? Thanks.
Todd Miller
Classic Products, Inc.
5/10/2011
Very attractive home. Interesting roofline. If you have areas where no ventilation is present, the breathable product could be a good idea. However, if you're leaving your old shingles in place, they really don't breathe much so the breathable underlayment will not help much if any. Also, keep in mind that metal roofing does not increase the need for breathability. Generally spekaing in most cases if moisture has not been an issue in the past it won't be in the future either.
Info @windowsonwashington.net
An informed customer is our best customer.
5/10/2011
+1 to Todd's recommendations. I don't think you will have any problems if you have not had any before. That all being said, breathable underlayment is not an expensive addition and will not appreciably increase the cost of the roof. Very cool home and roofline as well.
John Nguyen
5/11/2011
Thanks everyone for the advice and compliments. FWIW, I've settled on using GAF Tiger Paw for an underlayment. It's price about the same as most synthetic underlayments and I like GAF's claims about it, at least on paper anyway. I don't have any problem currently, so it's reassuring to hear I should be okay. Now for the fun decision - color. I'm torn between white, metallic silver, or galvalume. Any suggestion :).
Todd Miller
Classic Products, Inc.
5/12/2011
As far as color, keep in mind a couple of things ... If you're in an area with trees or other reasons for airborne dirt or fungus, a white roof will not remain fresh clean and white forever. Some of the mill finish or mill finish look roofs will not meet Energy Star requirements and be eligible for the federal tax credit. Additionally, they may lose reflectivity rapidly as they age. I know that many folks choose these lighter or shinier roofs for extra energy efficiency but in some cases a better choice is a medium or darker colored roof which has reflective pigment for energy efficiency.
Info @windowsonwashington.net
An informed customer is our best customer.
1/25/2017
Owens Corning studied this and produced this white paper on vapor permeance of the underlayment. http://www.owenscorning.com/NetworkShare/Roofing/10013915-Deck-Defense-Technical-White-Paper-October-2011.pdf

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