Thermal Stability of Underlayment

Guest User
What temperature can a wood deck reach underneath a metal roof? I ask this question in relation to the literature published by various manufacturers of underlayments stating thermal stability of their product to 260F. They don't state for how long (4 hrs, 12 hrs. etc.) their product is stable. Is there a building code or an industry standard for the thermal stability of self-adhering underlayment (temperature and time period)?
Guest User
I believe the nature of these underlayments is that the amount of time at a temperature is not the issue -- the maximum temperature is the issue. They just have a point where they start to break down. (So do I, I keep telling my kid!) Anyway, I digress. No, to the best of my knowledge, building codes to not cover this issue. I am unaware of the maximum temperature underneath a metal roof. It depends somewhat on the style of metal roof. The shake, shingle and tile profiles have an airgap between the metal and the underlayment. That helps. If you're in a real hot climate and you're looking at a metal roof that has a lot of contact between metal and underlayment, the extra investment in the High Temp underlayment probably makes sense.
Guest User
what and where do you get the high temp- underlayment? im wanting to put metal over shingles,felt strip for ventilation and the best way todo that is?
Todd Miller
Classic Products, Inc.
Underlayment goes over the existing shingles. If your metal roof will rest right against the underlayment and you're in a hot area, the high temp underlaymenst would be good to consider.
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