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Pancakes
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# Posted: 21 Nov 2022 02:57pm
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I'm going to be building a small A-frame cabin pretty soon (14x20).
Everything seems fine in terms of the plans.... EXCEPT not enough insulation for where I am (Maine).
Watching a few youtube videos, I saw some people putting insulation panels on the outside (2 or 4 inches) just on top of the rafters. Then on top of that zip sheathing.... and finally the roofing material.
They seem to have used these insulation washers on the insulation, then used long screws to tighten down the sheathing.
It just seems like putting a lot of weight onto the insulation? ((I was hoping to do mineral wool panels, since I hear polyiso doesn't do as well in cold climates?)
Anyhow, is this a good idea? Or am I missing something?
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ICC
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# Posted: 21 Nov 2022 07:59pm
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Standard XPS foam sheets (the pink or blue foam) has a load bearing rating of 15 PSI. That is 2160 lbs per sq. foot, more weight than any roof is likely to see.
Polyiso does have lowered performance in cold weather
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Tim_Ohio
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# Posted: 22 Nov 2022 08:07am
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If you insist on mineral wool, know that there is an ongoing debate as to whether it is or is not a carcinogen. Install it using all safety measures for your health, then cover it with something inside and clean up the dust mess that might accumulate during installation. It should be fine after encapsulated in a wall or roof. The clean up is key, though. You don't want the dust blowing about to be inhaled while you sleep or occupy the structure. A good quality shop vac should do the job. Be sure to filter the exhaust.
There is no reason to take a chance, even with particulates that are deemed safe. People take building materials for granted.
Tim_Ohio
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