MOVING AIR COMPROMISES R-VALUE?
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(Posted to cheap-shelters 5/04.)
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Doug posted: "I wouldn't think it would be compromised any more than, the R value of insulation in a conventional attic space that has ventilating air circulation, would be."
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Lots of attics -- even roof decks -- are vented but it's rather passive as there is a place for the hot air to get out but not much of one for cooler air to get in. I've heard attic temps should be no more than 10 or 15 degrees warmer than outside air on a reasonably warm day -- if that gives you any idea of how many structures are NOT properly vented. Once that attic gets
hot, the whole ceiling becomes a heater radiating that heat down into the living space -- a problem made worse by "decorators" who choose black or dark-colored shingles which turns the whole attic into a pizza oven from hell.
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It's my understanding that Fiberglas insulation is designed to function in a "dead air" space and that air moving constantly across the exposed surface of it will compromise R value, I just don't know by how much. This particular pallet gothic arch shape is anticipated to have unrestricted air entering at the bottom of
the roof/wall arch and exiting into the mini-attic and back outside from there. So it's a concern that the minimal R value -- at least initially -- not be compromised too much by the moving air.
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sail4free
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