Attic/insulation and vapor barrier


Old 06-22-08, 09:20 PM
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Question Attic/insulation and vapor barrier

Old house with attic, get to it from the outside, we have put down walkway as to not fall thru into house, we want to put insulation and vapor barrier, dont mean to sound iggy, but where do we place the insulation and vapor barrier? On the floor or up in the roof rafters and which goes down first? want to do it right, after removing all the old* what looks like wood chips and such... Any info would be greatly appreciated thankie
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Old 06-23-08, 03:41 PM
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Vapor barrier goes directly towards the heated side. Then the insulation, minimum is most areas of the country is 12-14" or R38+. You can install the vapor barrier and insulation in one process with insulation/vapor barrier integral w/the insulation. DO NOT insulate the rafter bays in the roof. That can cause major moisture/rot problems. From what you describe, I would vacuum out the old stuff. It is likely not fire resistent or of good insulating quality.
Old 06-23-08, 05:36 PM
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My 2000 IRC says the vapor barrier goes on the warm-in-winter side except:
-where moisture or freezing will not damage the materials,
-where the framed cavity is vented to allow moisture to escape
-in counties identified with footnote a in table N1101.2

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Old 06-23-08, 06:12 PM
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would not worry about the VB. You can't make it continuous do to the ceiling being finished so it will have to many gaps to make it worth while.
Old 06-23-08, 06:48 PM
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If you live in a cold climate, then the vapor retarder goes toward the heated side. As previously indicated, you can purchase batt insulation with attached vapor retarder that is supposed to be installed with the facing downside toward heated space below. If you opt for blown in, then plastic vapor retarder is installed first.

What is very important is that all gaps around perimeter, vents, ducts, chimneys, or whatever that could possibly allow warm, humid air to pass from below into the attic be sealed before you insulate. Small gaps can be sealed with silicone caulk. Large gaps can be sealed with spray foam insulation.

As indicated, remove the wood chips from the attic. They may be tempting to insects, and they provide poor insulative qualities. Also, do not insulate attic ceiling.

Just as important as insulation is ventilation. Do you have adequate ventilation? Hot air in attic has to have a place to go. Without adequate ventilation, built up heat can shorten roofing life span and increase energy costs.

If in doubt, contact your local Building Code office. They will update you on the minimal requirements for required insulation in new construction. Further research may reveal that you actually need more. Do your homework and don't let the dog eat it.
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