Leaky synthetic roof underlayment
Hello everyone –
We have a multifaceted problem with our roof underlayment and are looking for some professional opinions.
We ran out of time to get our originally spec’d underlayment back in December and ended up using Owens Corning ProArmor synthetic, as it was stocked locally. Now, we face a few problmens:
- It says for shingles only. We are putting on pro-panel metal.
- It has a 4 month UV exposure rating and we are now in the 5th month. It appears to still be holding up fine (it’s been winter exposure, north facing), but I’m not sure about long term durability.
- It has leaked quite substantially, especially in certain areas, to the degree that a heavy rain leaves pools of standing water in areas of the house. I was sure there were some substantial tears, etc. but upon inspecting, my only conclusion is that the numerous staple penetrations must be the culprit. We had a failing stapler and as a result put in far more than normal, since few would bite. Again, this was exacerbated by the time constraint.
What would you guys suggest in this situation? Options I’ve considered are:
A. Rip off the current underlayment and put down new, metal roof compatible underlayment. I originally spec’d grace tri-flex 15.
B. Put down an additional layer of 15# or 30# felt paper with minimal fasteners immediately prior to installing permanent roof
C. Put an additional strip of underlayment under each lap with minimum fasteners to seal staple penetrations immediately prior to permanent roof install.
D. Leave it be. Logic being, we are in the desert and the underlayment is more for condensation than roof leaks.
While A is the most sound option, it’s worth noting that we are building this house out of pocket and the budget is extremely tight. The $180 invested in the two rolls is therefore worth considering, even if it’s ultimately a drop in the water.
Thanks so much for the help!
Cheers,
Zane
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Replies
Hi Zane -
Even in the desert, water management, especially on a roof, rules. I am going to be that unless you are doing the roof cladding yourself, just about any roofing contractor you can get to work with you is going to make you redo the roofing underlayment. Just too much exposure and penetrations for a contractor to take on as liability.
If you are doing your own roof cladding install, I would still only use compatible materials UNLESS you can get a roofing professional who regularly works with the underlayments in question to "sign off" on the combo.
Peter
Peter - I have been meaning to thank you for months now for your reply. I am going to take your advice and redo all the underlayment. We just now finally got our metal roof ordered, so it's time to get down to it. Our hardware store makes the options pretty simple:
1. Good old 30lb felt
2. Grace triflex XT
Price is approximately the same for both. I read Martin's post about best roof practices where he recommended felt paper if it's getting covered quickly, because it can breathe. I believe the grace is warrantied longer.
One final question: the roof manufacturer said we don't need to butyl tape the metal roof laps (standard RIB profile) on a 4/12 pitch. I figured for the little added cost, it's good insurance. What's the consensus here?
Thanks everyone!
Zane
Roof underlayments are not designed to be the main source of bulk water rejection. That is what the metal roof is supposed to do. The underlayment is a back up source for minor roof leaks which can happen around penetrations or if the water somehow overtakes the standing seam and drips down. Nobody makes a roof underlayment that is designed to be the main source of water infiltration protection.
With that being said. It might be a good idea to replace the underlayment now for peace of mind. It's cheap insurance to replace it now.
Is the metal roof screwing down onto the decking (exposed fastener) or is it a standing seam roof with purlins that clip onto the purlins (hidden fasteners)?
Thanks Peter!
The roof is exposed fastener, classic RIB profile, self tapping rubber washer screws. Seems to be what about 95% of metal roofs are around here, though you do see the occasional standing seam.
So I've called around to a bunch of yards/hardware stores and no one seems to stock ASTM D226 felt paper. The big box stores have the stuff for wrapping walls, but it seems almost obsolete. Even the local roof companies only stock synthetic. Have you guys had the same experience?
I was planning to lay down double 15# felt for our 4/12 exposed fastener metal roof.
The most critical aspect of metal roofing underlayment is to prevent the underside of the panels from getting scratched from sheathing. Tar paper deteriorating before the 40 warranty is no good for me. Synthetic paper provides no scratch protection. Use what the metal company sells.
Just a note 6 months after this post was made, but we've had similar experience with Tyvec Protec 160 underlayment. 4/12 roof pitch and perhaps 20% of the staples are not capped and we have got leaks all over the place. This was during a high rain, "atmospheric river" event in Sonoma County, CA. We are about a month from having the metal roof on so we are just going to go forward and deal with it. I was shocked at how much water has moved through the underlayment but based on Peter's comments that seems per design specs. Also of note this underlayment has endured the high winds during the period of the Kincade fire that nearly burnt our small town. Gusts up to 60 mph here. Now that I think about it I can imagine how all the jostling from the high winds could create micro-openings around staple holes. Now we've got epic rainfall quantities in an hour and sure, the underlayment is overloaded and leaking around staple holes. Makes sense. Just posting this in case it helps anyone else.