So I Need A Vapor Barrier - Insulation - DIY Chatroom Home Improvement Forum

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Old 09-20-2013, 07:53 AM   #1
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So I Need A Vapor Barrier

My house is like this - Vinyl siding to 1/2 inch fan fold foam board to house wrap to wall boards to 2x4 studs I will be extending the studs to 2x6 and fitting in Roxul R23 comfort batt. Once I put the Roxul in the the studs do I need to put on a 6mil plastic wrap for vapor barrier or do the other items i mention act as a vapor barrier? Central Maine is my loaction.


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Old 09-20-2013, 08:11 AM   #2
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I would not do it, I believe that would form a double vapor barrier.


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Old 09-20-2013, 12:23 PM   #3
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No. You already have an R1.5 3/8" thick vapour retarder on the outside and whatever you put up on top of the Roxul would be another vapour retarder. So the ability of vapour to travel inside to outside and/or outside to inside is reduced sufficiently to avoid condensation.

However, I'd put up gyproc walls and paint them - properly - with latex paint to have a good vapour retarder on the inside. Caulk the gyproc panels to the studs using sealant to reduce air movement - which is what does the carrying of the vapour.
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Old 09-20-2013, 06:19 PM   #4
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The fan-fold (1/2") may have a perm rating of 1.1 Perms;,d.cGE

For your location, Zone 6;

With over 1 perm at sheathing, you are vapor semi-permeable and require asphalt faced paper, SVR, or v.b. paint next to the drywall, Fig.4a:


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