# insulate & vapor barrier around electrical box



## acerunner (Dec 16, 2009)

exterior walls require insulation & vapor barrier. Electrical boxes on exterior wall breaks the vapor barrier if the box itself is not sealed. How do I maintain a sealed vapor barrier around the box? I've seen vapor barrier wrapped behind the box, but I dont understand where the cables would come in from. The cables will have to also poke a whole through the vapor barrier, so how do you seal that around the cables?


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## teamo (Sep 7, 2008)

I believe they make a plastic box that is nailed to the studs and then the electrical box is installed inside of this. It gets sealed with foam or silicone for the penetrations and the vapor barrier is sealed to the face of the box with silicone.


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## secutanudu (Mar 15, 2009)

I had this same question actually. I've seen some stuff that Mike Holmes uses, it's like a rubbery material that is wrapped on the back of the box. Any idea what this is or where to get it? Maybe a supply house would have it.

What about using the foam weather stripping behind the outlet? That would block a fair amount of moisture, right?


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## baum (Jul 14, 2009)

Check your big box stores. I found at one near me a molded plastic (6-8mil) that has flanges incorporated into it. Then you just tape your VB to it. 

see pic:
http://images.google.com/imgres?imgurl=http://www.homedepot.ca/wcsstore/HomeDepotCanada/images/catalog/BCVB1_4.jpg&imgrefurl=http://www.homedepot.ca/webapp/wcs/stores/servlet/CatalogSearchResultView%3FD%3D977583%26Ntt%3D977583%26catalogId%3D10051%26langId%3D-15%26storeId%3D10051%26Dx%3Dmode%2Bmatchallpartial%26Ntx%3Dmode%2Bmatchall%26recN%3D112051%26N%3D0%26Ntk%3DP_PartNumber&usg=__sokZEMKo23Vvnhcimd2dAuHLntE=&h=400&w=400&sz=11&hl=en&start=4&sig2=kK-vHeKMtvwkWKTUJfh_HQ&um=1&itbs=1&tbnid=F3z1N6OAH2ZfrM:&tbnh=124&tbnw=124&prev=/images%3Fq%3Delectrical%2Bbox%2Bvapor%2Bbarrier%26um%3D1%26hl%3Den%26sa%3DN%26rlz%3D1T4GGLL_enUS315US315%26tbs%3Disch:1&ei=VtvVS_eZHcO78gatw6WrDwhttp://www.21stcenturyent.com/catalog/images/ACPR0001.jpg


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## acerunner (Dec 16, 2009)

teamo said:


> I believe they make a plastic box that is nailed to the studs and then the electrical box is installed inside of this. It gets sealed with foam or silicone for the penetrations and the vapor barrier is sealed to the face of the box with silicone.


thanks. I found one such box here: http://www.lessco-airtight.com/
But with that, you would still need to find a way to seal the hole where the wire come through this box. In the picture, looks like they taped it or something. I think a putty or silicone (as you mentioned) would work well here.


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## secutanudu (Mar 15, 2009)

They don't sell these at my local big-box store or electrical supply house. I don't have time to order one - think plastic wrap on the backside of the box with the foam underneath the cover plate will suffice?


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## acerunner (Dec 16, 2009)

secutanudu said:


> I had this same question actually. I've seen some stuff that Mike Holmes uses, it's like a rubbery material that is wrapped on the back of the box. Any idea what this is or where to get it? Maybe a supply house would have it.
> 
> What about using the foam weather stripping behind the outlet? That would block a fair amount of moisture, right?


Yeah, I saw that episode. It was like a sheet of putty that he wrapped around it. Sealed right around the wire and everything. That episode was about sound deadening insulation, so I assumed the wrap was for sound deadening, but the same concepts apply to thermal insulation as well.


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## Gary in WA (Mar 11, 2009)

http://www.buildingscience.com/docu...sheet-310-vapor-control-layer-recommendations

http://www.ecohomemagazine.com/energy-efficient-design/a-close-look-at-common-energy-claims.aspx

Be safe, Gary


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