Vapor Barrier Is Not A Air Barrier Make! It Is A Vapor Retarder - Insulation - DIY Chatroom Home Improvement Forum
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Old 04-16-2014, 09:35 AM   #1
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Vapor barrier is not a air barrier make! It is a vapor retarder


After explaining till I was blue in the face with a home owner that was up set with me for not using faced batts. because then the home is not air sealed. I finally had to take a piece of sheetrock place it over the exhaust of my shop vac and ask HO how much air is getting through the sheetrock???? um none was there reply. Exactly! Kraft facing poly are vapor retarders not barriers they are not interchangeable meanings a vapor barrier is about 6 mill thick and up a vapor retarder is about less than 4 mil thick. and lets moisture vapor to escape the house one way and not enter the other way. house wrap is a retarder as is plywood. In fact the HO had the county building inspector come over to give me a talking to. for non using paper faced insulation. the inspector told them the house has tyvex wrap 5/8th plywood sheathing it has a vapor retarder to let the water vapor out.
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Old 04-16-2014, 09:11 PM   #2
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Old 04-19-2014, 02:29 PM   #3
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Yes, vapor barrier/air barriers can be confusing. Code requires a vapor barrier directly under the drywall- depends on the class. Asphalt coated paper is a Class 2 VAPOR barrier, drywall is an AIR barrier- two different design solutions. The faced batts retard moisture- drywall lets moisture diffuse through it but stops air. http://publicecodes.cyberregs.com/ic...9_6_par004.htm

None of the vapor barriers/retarders let moisture through one way only- if they are permeable (retarders)- it is both ways, including housewraps. Paper-faced insulation (vapor permeable) is the code-required vapor retarder, house wrap is the required Water Resistive Barrier (vapor permeable) on the outside of cavity, and plywood/OSB is the required structural sheathing (vapor permeable)--- unless it is Advantech sheathing. http://publicecodes.cyberregs.com/ic...9_6_par005.htm

In a heating climate, codes require the vapor barrier/retarder under the drywall to stop/slow outward bound moisture. Homeowner is correct. Is this in Oregon?
http://publicecodes.cyberregs.com/ic...9_6_par006.htm

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17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?
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Old 04-21-2014, 07:23 AM   #4
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It is in washington state and the county I work and live in does not require any form of vapor retarder between the sheetrock and insulation because they found it is a habitat for mold growth. no poly is required no kraft face no nothing. they feel two coats of PVA primer is sufficiant.
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Old 04-21-2014, 07:02 PM   #5
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Yes, specific vapor retarding paints are acceptable in WA, though I have seen workers apply them similar to regular primers- just coat the wall. Most are very specific about thickness/coverage of application, ranging from 6-12+mil and 120-400 sq.ft. per gallon. Hence the clause; "Materials must be applied in accordance with the manufacturer’s instructions to achieve specified permeance ratings." from our WA guide; http://www.google.com/url?sa=t&rct=j...,d.aWc&cad=rja

It is code accepted, just not widely known; http://www.ecohome.net/guide/painting-vapour-barrier

Shame on the inspector for not explaining it correctly to the HO.

Gary
PS. a good local study for WA (PVA primer included); https://docs.google.com/viewer?a=v&q...NmmYf-psHZnLA;
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Last edited by Gary in WA; 04-21-2014 at 07:08 PM.
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