rockies
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# Posted: 15 Jul 2016 07:57pm - Edited by: rockies
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This is an excellent article on "Dew Points".
http://www.greenbuildingadvisor.com/blogs/dept/musings/are-dew-point-calculations-rea lly-necessary
In another thread the proper way to insulate a cathedral ceiling is being discussed (which is usually the type of ceiling or "roof" that most small cabins end up with).
I tend to be a fan of spray foam applied to the underside of the roof sheathing. There are many basic problems with batt insulation (whether roxul or fiberglass) the main one being the movement of air and moisture within the batt. No matter how thick the batt the moisture will always move through it and condense on the coldest surface (the underside of the roof sheathing).
Spray foam is regarded as insulation, air and vapor barrier in one. The main advantage is that it raises the temperature of the sheathing above the dew point so that any moisture in the roof assemble won't condense on the sheathing. Since the spray foam insulation effectively prevents moisture from escaping to the outside I would recommend that moisture should be allowed to escape to the interior of the cabin. If it gets in it has to get out.
I'll try to find some more articles on this.
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