“Hot Roof” underlayment for metal roof

We’re building a house with spray foam insulation and an unvented roof (conditioned attic space). We’ll be putting a corrugated metal roof over this. My question is, what’s the best kind of underlayment in this situation? Does it need to be permeable or impermeable? The house will have a heat recovery ventilator. We’re building in a cold, dry climate–but summers still hit 100, occasionally.
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Greetings badlybent,
This post, in response to your question, will bump the thread through the 'recent discussion' listing again which will increase it's viewing.
Perhaps it will catch someone's attention that can help you with advice.
Cheers
Peach full,
easy feelin'.
Bump
tarpaper is fine
rooftopgaurdII is better
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tarpaper is finerooftopgaurdII is better
Personally, I prefer Titanium or Permafelt (another similar product), but I wonder what's going to happen to the synthetics in this situation. I once tore a 3-4 y/o metal roof off to find they had used Tyvek as an underlayment. This was indicative of all the other things wrong with the installation that lead to the replacement of the roof. But, the Tyvek had deteriorated to the point that e were not able to remove a piece of it bigger than a quarter. This was a golf course home and it looked like snow in July on the 7th fairway.http://grantlogan.net/
I refuse to accept that there are limitations to what we can accomplish. Pete (I am so in love with myself) Draganic
But, the Tyvek had deteriorated to the point
So, as a guess, they had not used the tyvek specifically makes for roofs?
I get the fliers begging me to specify this stuff, but I've never seen the detail for how it starts & stops, especially if the attic is supposed to be vented, and we are using their housewrap . . .
I have this feeling that tyvek will wind up the duct tape of the future--everyone will know someone who swears by it, and no one will exactly know how it's supposed to be used.Occupational hazard of my occupation not being around (sorry Bubba)
Mine was done with Titanium.
When the metal roofing gets warm, especially under a hot roof, tar paper will melt and adhere to it, soon deteriorating. Grace makes an underlay for metal roofs "Triflex 30". It will keep the roof watertight for 6 months without the roofing, is next to impossible to tear and is great to walk on. Several other companies make similar synthetic underlays. They are the way to go under metal.