Melting Self-Adhering Underlayment, Next Steps?

The self-adhering underlayment (GAF stormguard) on my 8 year old roof in Houston, Texas is melting and seeping down the shingle nails, leaving globs of tar about the size of nickels in my attic (including the top of my brand new furnace)! Underlayment was installed across entire roof. Roof is 5:12 pitch. Shingles are GAF 30-year HD architectural (Timberline HD w/ algae guard). Attic is ventilated with ridge vents (cobra 3) and soffit vents. Decking is 3/4" shiplap with no radiant barrier. There are no shiny mirror glass skyscrapers shining on my roof. Anyone have experience with this (what appears to be product failure/material defect). I just filed a claim with GAF. Obviously I need to remove this roof if I want to stop tar from leaking all over my attic. Should I expect to replace the decking as well? I realize this will probably be a field decision when roof is torn off. Just trying to set my expectations. Any thoughts appreciated. Next roof will use traditional #30 felt for underlayment.

Do you have any pictures?. Is it only dripping off of the nails or is it also coming through the plank spaces?

If it is melting to the point you are describing is is going to be fully fused to the deck, if you want the drips to stop you would need to remove the decking.

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Dripping through nails and plank spaces. Just uploaded a couple of photos.

I’ve only seen that happen under metal roofs

Yep. That is probably the reason for the “high temp” versions of this product being recommended and specified for metal roofs. Houston’s climate is hot, but it’s not like it is as hot as Phoenix. I’m guessing the conclusion will be: I got a bad batch of GAF Stormguard.

You are correct that this is not what we want our ice and water shield underlayment to be doing.
Dripping into the attic.
But at the same time, what is the harm
Done?
The product is doing its job of making the roof leak free.
Ill bet there were many shingle nails that missed the wood between the boards and it is the underlayment that is keeping it from leaking.

I would leave this roof alone until it wears out
The next roofer is going to have mission impossible on his hands…

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