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Can Insulation have vapor barrier built into it?


BillyDIY's Avatar
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Join Date: Aug 2008
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11-23-08, 12:28 PM   #1  
Can Insulation have vapor barrier built into it?

While tearing down ceramic tile and rotted drywall in a bathroom shower repair I noticed that the pink fiberglass insulation had some slight black mold growing on it, so I am opting to replace those columns.

My house was built in the late 1970s and I noted that all of my exterior walls including this bath one had a aprx 2-3 mil thick piece of clear plastic over top of the insulation which I assume is the vapor barrier. This bathroom insulation appears not to be "faced" in that it is pink on both sides (no paper on one side).

I have 2x4 outside wall construction so I purchased R-13 PinkPro or ProPink insulation. Because this is the "good stuff" and is "faced", do I need to put a 2-3 mil thick sheet of clear plastic over top of it? Is this specificially the vapor barrier or can you purchase pink insulation that has a vapor barrier built in?

It is my assumption that because this is "faced" that if I staple the faced part interior so I can see it that is all I should require.

If it matters I will be putting cement board over top of the insulation when I redo the shower stall.

If I need to 2-3 mill plastic for a vapor barrier any special thing I should ask for at HD or Lowes? When I did this today, they pointed me to the drop clothes in the paint area.

 
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airman.1994's Avatar
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11-23-08, 05:55 PM   #2  
Very common for people to think that paper faced insulation is a VB. The paper does not have a high enough perm rating to be a VB so yes you should add the 4mil VB. If they make insulation with the ploy on it I have never seen it. I would think it would be easier to add it at the end than to have to sell each piece to the next.

 
BillyDIY's Avatar
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11-23-08, 07:10 PM   #3  
Thanks airman. The ploy actually came from the Lowes guy whom after I asked about the plastic sheet said something paraphrased "the liner of the insulation has tar built into it which acts as a moisture barrier".

Is there anything special about the clear plastic sheet other than it is 4 mil?

 
BillyDIY's Avatar
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11-23-08, 07:26 PM   #4  
After some further investigating, it appears that the Lowes guy was right. Supposedly if you have kraft faced insulation it does act as the barrier.

Save Energy: Question: If we buy Kraft-faced insulation will we need to install a plastic vapor retarder over it?


I guess there could be a debate if you should use faced or no face with the 4 mill poly or not. Since I already have the roll I'll probably just use it.

 
vidiot's Avatar
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11-24-08, 11:53 AM   #5  
Posted By: BillyDIY I guess there could be a debate if you should use faced or no face with the 4 mill poly or not. Since I already have the roll I'll probably just use it.
Technically the (coated) kraft face and 4 mil poly are both vapor retarder's, not barrier's. But what ever you call it, all you need if the kraft faced insulation. It's never a great idea to have two vapor barriers (as you can trap moisture between the two), but it shouldn't be a problem as long as they are at the same depth in the wall.

 
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