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-   -   foam over batts (http://www.diychatroom.com/f103/foam-over-batts-123383/)

Ram Guy 11-13-2011 11:22 PM

foam over batts
 
I am looking to develope my basement. The exterior walls are framed and insulated. The vapor barrier leaves A LOT to be desired!! I was going to pull all the vb and insulation and just spray foam the concrete walls...now I'm thinking of leaving the R12 insulation and putting 2" foam board over the studs for the vb (ship-lap and taped). Is there any good reson I can't do this? I should end up with about an R30 and 2" of foam works as a vapor barrier...Am I missing something or is this a good idea?

Thanx

Windows on Wash 11-14-2011 11:06 AM

Where is the home located?

Foam applied directly the concrete will be much more effective.

user1007 11-14-2011 05:42 PM

Most 2" foam board is not fire rated and in some instances can be a real fire hazard. You will probably be in violation of fire codes. Even if you sneak it in and something goes wrong? Your insurance company will have a great reason to deny a fire claim.

Ram Guy 11-14-2011 09:06 PM

Quote:

Originally Posted by sdsester (Post 771185)
Most 2" foam board is not fire rated and in some instances can be a real fire hazard. You will probably be in violation of fire codes. Even if you sneak it in and something goes wrong? Your insurance company will have a great reason to deny a fire claim.


I agree, also no more or less than spray foam is fire rated...but the drywall will be. I don't plan to leave the walls bare. It will simply be batts in a studded wall, 2" foam board on the studs over the batts, drywall over that.

Also I understand that idealy I would want the foam right on the concrete but in this case the exterior walls are already studded...can't really get the foam in there now unless I spray foam it $$$$$. And I don't want to rip the studs out either...

mnp13 11-15-2011 09:43 AM

If those bats are right up against the concrete, I'd check them for mold.

TimMauriello 11-15-2011 05:26 PM

Agreed. The first problem is that you don't want a vapor barrier over bats in a basement as that will trap moisture coming off the concrete. Using xps as the vb that way may make it worse if it moves the condensation point into the fiberglass.

Do you have any space behind the studs?

Have you looked into the DIY spray foam kits? Like foamitgreen.com? Moe expensive than xps, but it would seal tight to the studs and even if you only got an inch in there, you could use bats on top.

I've never used it and I haven't seen much in the ways of review here, but from what I understand of spray foam, this might work and not be too much more expensive than xps sheets with tape, caulk, etc.

Ram Guy 11-15-2011 06:13 PM

Quote:

Originally Posted by TimMauriello (Post 771978)
Agreed. The first problem is that you don't want a vapor barrier over bats in a basement as that will trap moisture coming off the concrete. Using xps as the vb that way may make it worse if it moves the condensation point into the fiberglass.

Do you have any space behind the studs?

Have you looked into the DIY spray foam kits? Like foamitgreen.com? Moe expensive than xps, but it would seal tight to the studs and even if you only got an inch in there, you could use bats on top.

I've never used it and I haven't seen much in the ways of review here, but from what I understand of spray foam, this might work and not be too much more expensive than xps sheets with tape, caulk, etc.


VB is code here...Using foam board is a much better VB than improper poly in my opinion. I have looked into those DIY spray foam kits, and they are definatly pricey. I don't know that they are MUCH cheaper than getting the pros to spray it.But I appreciate the input.

Gary in WA 11-15-2011 08:44 PM

Rigid foam board stores moisture going through the concrete wall to release it slowly drying to the inside. An air permeable insulation as f.g. will not slow any moisture. In fact the dew point will change from the concrete/f.b. to the f.g. because you have moved it from concrete to the interior side. Your f.g. will get wet and lose 60-70% of the R-value: http://www.nrc-cnrc.gc.ca/eng/ibp/ir...ling-heat.html
The paper facing will mold: http://www.inspectapedia.com/sickhou...rglassMold.htm

The correct way: http://www.buildingscience.com/docum...ts?full_view=1

Here is the problem: http://www.buildingscience.com/docum...researchreport

The foamboard will stop about 91% of the heat loss making the cavity colder (yet warm enough to mold), it needs to be next to the concrete: 2” foamboard = R-10= 2.78” of f.g. @ 3.6: http://www.enersavesystems.com/pdf/E...Insulation.pdf

Where are you located, as already asked? Looking for a State/Providence, not physical address…

Gary

Ram Guy 11-15-2011 09:49 PM

Thanks Gary. And I'm in Calgary Alberta.

Gary in WA 11-15-2011 10:23 PM

Ahhhh.... another member from up North. http://www.diychatroom.com/f103/insu...34/#post769065

Check locally, they may require a basement v.b. unlike here in the U.S. Though reading the sites, you do have some foamboard with strapping- no vapor or air barrier, depends on your basement Class finishing per Code.

Gary


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