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Crawlspace fiberglass roll insulation..Kraft face or NO ?

Crawlspace fiberglass roll insulation..Kraft face or NO ?


Old 02-05-17, 09:34 PM
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Crawlspace fiberglass roll insulation..Kraft face or NO ?

We are in southern OR and have a vented crawlspace now insulated with un-faced rolled fiberglass. There is 6 mil plastic on the soil and duct work in the crawlspace.

I have been reading conflicting articles about rolled fiberglass in a crawlspace in the floor joists: Some say use Kraft paper faced rolls with the paper facing up to the sub-floor. Other articles say use un-faced only.

What is the correct way to go, please ?
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Old 02-06-17, 03:29 AM
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There should be a vapor barrier on top of the insulation, but you have a vapor barrier on the dirt. My recommendation would be to use Roxul and not worry about the moisture. Hang in there as there are different schools of thought on this and others will comment.
Old 02-06-17, 07:08 PM
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Vapor retarders are designed to slow the migration of water vapor from an area of high concentration to an area of lower concentration but it is really only of critical concern when the transfer could potentially result in condensation. Condensation will occur only if certain conditions with regard to temperature and vapor saturation are met.

With regard to your situation, a vented crawl space will be an ever changing environment due to the temperature and moisture variables introduced by incoming outdoor air.

It it unlikely you would suffer any consequence by not having a vapor retarder on the top of your insulation. The moisture level in air within your living space will unliklely be routinely higher than the moisture level in the crawl space.

You may be better served by making sure you seal any penetrations in the floor assembly for mechanical and electrical lines. That would prevent air from the crawl space from being drawn into the living environment and help to limit the stratification of air temperature planes . This is what typically causes an environment of cool temperatures on the first level and warmer temperatures on an upper level.

If you have a ducted heating/cooling system with ductwork in the crawl, you may want to consider using foam, preferably spray applied, on the crawl space walls and eliminate the venting. This approach considers the crawl as a semi conditioned space. You would eliminate the floor insulation.

You should, of course, review the ductwork and seal any joints with an appropriate joint sealant material.
Old 02-22-17, 02:01 PM
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Had a licensed contractor use JM un-faced R21. Thanks for your comments.
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