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June 6, 2012 | Show All

BIBCA Member Needs Advice on Air Infiltration

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If 6 mil vapor barrier is installed over the top of sheetrock on a ceiling, will this combination provide the same or similar air infiltration benefits as sprayed polyurethane foam?

 

Posted At : 3:22 PM. | Posted By : KRISTIN | Link | | Comments (6)

Could be better. The foam will provide thermal resistance, but the foam can crack and/or shrink. A continuous sheet of 6 mil polyethylene is also a water vapor retarder. Dave Yarbrough R&D Services

Posted By DAVE YARBROUGH / Posted At 6/6/12 3:45 PM

Be VERY CAREFUL about doing this in terms of the climate you live in. Doing what you suggest in a hot humid climate where the vapor drive is towards the interior 9 - 10 months a year will cause condensation and promote biological growth. Obviously in other areas where the dynamics are different that may not be the case.

Also in regard to the comment on foam cracking or shrinking that would be an installation error from the spray foam contractor. Done correctly with high quality product that does not happen.

Posted By LOUIS TRIAY / Posted At 6/6/12 4:27 PM

I think spray foam would still do a better job because it actually bonds to the wood and sheetrock where the poly is just attached with staples in a few places. The staples actually penetate the poly lowering its benefits. The same is true for the sheetrock screws and nails. However, if cost matters, it is a good way to go vs. spray foam because you do get a good benefit from it.

Posted By DEAN MOODY / Posted At 6/6/12 4:53 PM

Coming from a Bibs / Spray foam installer. It's hard to compare 6 mil poly with spray polyurethane foam. Sorry in my mind there is no substitute for 2# foam. Rouse Insulation

Posted By KEN ROUSE / Posted At 6/6/12 6:52 PM

The last 2 homes we have built have tested at 150cfm at 50 PA or less. These homes are 1800 sq. ft. with 9' walls and we have been told by the Energy Star system in Wisconsin that these are the tightest homes in the state. They are BIBS homes. I have tested foamed homes and they can be tight but it depends on the installer. The same is true of installing the vapor retarder. Details matter.

Posted By TIM JOHNSON / Posted At 6/6/12 8:05 PM

Polyurethane would be better becauce there will not be air space beween the sheetrock and the air berrier. The other way there will always be a possibility that the heat and cold can meet it will make condensation.

Posted By GERALD BERNIER DRUMMOND INSULATION LTD / Posted At 6/7/12 8:37 AM