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bf514921 08-13-2012 02:09 PM

Does Closed cell insulation require vapor barrier?
i had closed cell spray foam installed in my basement. Its 2 inch thick on the walls and 3 inch in the rimm joist. I live near cedar rapids iowa, zone 5 almost 6 i think. Does haveing the closed cell foam 2 inches thick provide a vapor barier, or vapor retarder? Do i need to install a vapor barrier over the spray foam?

Windows on Wash 08-13-2012 04:28 PM

Who is the manufacturer on the foam? Your SPF contractor should have the perm ratings but 2-3" usually qualifies as a vapor retarder.

bf514921 08-13-2012 04:41 PM

gurdian 55 , its listed as a class 2 vapor retarder at 2inches , its permeability is 1.98 perms @ 1 inch, it doesn't list at 2 inches. but this is a retarder - not a barrier, which is why i ask the question if i still need a vapor barrier.

Windows on Wash 08-13-2012 07:38 PM

Class II is fine.

Make sure you drywall is airtight and you are 100% fine.

bf514921 08-15-2012 08:31 PM

all it says for 2 inch is under 1 perm for the guardian, figures its good

Gary in WA 08-15-2012 11:56 PM

The foam is air-tight to seal the concrete;

The latest on foam perms in a basement;

Some ccSPF is 1.5perms per inch, 1/2 that for 2" = 0.75 perms about the same as plywood.
Yours is 0.99 perms.


bf514921 08-17-2012 09:31 AM

GBR, thanks for the links i was reading the green science one and this quote answers my question i think
"Here’s what I wrote in response to Baumgarten’s question: “I have puzzled through the same question, and I have concluded that there is no reason for a foundation wall to dry to the interior, in spite of what you sometimes read. Walls insulated on the interior with closed-cell spray foam perform very well — and they certainly don’t dry to the interior.”"

my walls in the basement are closed cell foamed, i dont think any air will get close to the foundation spray foamed part of my basement. The more i read i think the more i think i made a good choice in waiting saving and having the pray foam installed.

GBR, thanks again for all the helpfull links, i have read may other posts where you provided useful info.

Windows on Wash 08-17-2012 04:19 PM

ccSPF is a great option.

Rigid foam can also be applied if any customers are thinking about doing a basement insulation project in the future as well. It is a bit more labor intensive to be done correctly but it is an option in most cases.

Gary in WA 08-18-2012 11:30 PM

Well, I think you made the best choice with SPF on the concrete/rims. That is the fastest, best, and easiest way for a homeowner to do (not the cheapest or very DIY friendly). Many times, especially on older concrete walls, the surface is irregular and with extra concrete (from the form gaps) on the surface. Many times the wall is not “in plane” but has kinks or bows from the forms shifting during the initial pour. This makes gluing rigid foam board very difficult to get a perfect air-seal. Even the glue pattern is important, resulting in convective loops to redistribute the heat/moisture on the wall surface back there; as little as a 1/16” gap can let in moist basement air to condense;

The drywall gaps around electrical boxes/switches, gaps under the p.t. bottom plate without a foam poly sill sealer, and gaps at the wall/joist cavities at floor above should all be air-sealed perfectly. One could also use rigid in 1" layers or less, to build-up while following the wall contours more closely. OTOH- with SPF you stop the air (only once required) at the concrete, especially with a professional application. The result is a vapor retarder/air barrier/thermal break that is worry free and durable for a long term solution.

I have no idea why that zinger was thrown at you when you have already done SPF? Maybe it was at me, or maybe he forgot you already applied it (been there, done that, LOL)... WoW?

If you expect high RH in the basement without a mechanical means to remove it, I would suggest adding a vapor barrier paint primer on the drywall after taping/texturing, this will help guaranty less moisture from the basement to the cavity. E.G.- page 29 in the first link I gave is similar to your wall only with 1” of foam and the paint worked well.


Windows on Wash 08-19-2012 07:32 AM

Forgive my post.

I misread where you have already applied the ccSPF in this case.

It is the best option but not always the most DIY (given the site) friendly or cost effective.

Thanks for posting up and keep us updated with pictures.

bf514921 08-19-2012 10:49 AM

i went with the spray foam to help me eliminate any concers related to vapor barier, moisture and mold. my basement is dry to begin with, but i dont like the though of mold/mildew and possibly condensation issues. also in my case compared to traditional methods of insulation, this was more costly but my energy company offered a rebate that will cover part of the cost, and if the energy credit still exists for 2012 will breing the cost down considerably closer to using traditional methods of batt insulation or foam board.

also as a side note, even if you do not have spray foam installed in your basement on the walls, do consider even a diy kit for the box sil/joist area/whatever you may refer to it as. the spray foam is awsome in this cavity, filled it completely and makes a great airtight, and highly moisture resistant barrier. closed cell spray foam of course.

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