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Closed vs open cell foam

skippy | Posted in Energy, Heating & Insulation on November 9, 2008 12:10pm

What’s the difference between open cell vs closed cell foam insulation?

How is water based vs urethane based different?

Thanks

Skippy

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  1. reinvent | Nov 09, 2008 12:45am | #1

    Polyurethane Foams

    All closed-cell polyurethane foam insulation made today is produced with a non-CFC (chlorofluorocarbon) gas as the blowing agent. This gas doesn't insulate as well as insulation made with a CFC gas, however it is less destructive to our planet's ozone layer. Foams made in this way have an aged R-value of R-6.5 per inch thickness. Their density is generally 2.0 lb/ft 3 (32.0 kilograms per cubic meter [kg/m3]). There are also low-density open-cell polyurethane foams (0.5 lb/ft 3 [ 8 kg/m3 ] ). These are similar to conventional polyurethane foams, but are more flexible. Some low-density varieties use carbon dioxide (CO 2 ) as the blowing agent.

    Low-density foams are sprayed into open wall cavities and rapidly expand to seal and fill the cavity. There is at least one manufacturer who offers a slow expanding foam. This type is intended for cavities in existing construction where there is no insulation. The liquid foam expands very slowly and thus reduces the chance of damaging the wall from over-expanding. The foam is water vapor permeable, remains flexible, and is resistant to wicking of moisture. It provides good air sealing and yields about R-3.6 per inch of thickness. It is also fire resistant and will not sustain a flame upon removal of the flame source.

    1. skippy | Nov 09, 2008 02:51am | #2

      Open is water vapor permeable and closed is not?

      Which is the recommended for new construction in walls?  If one over the other-why?

      Thanks- Skippy

      1. reinvent | Nov 09, 2008 05:08am | #3

        Closed cell gives you roughly twice the R value per inch so a better performer. But it is also roughly twice the cost of open cell. Even more important than R values of both types eliminate air leakage.
        If you can afford closed cell go for it. Both will make the house quieter too. There is also tax rebates available.
        I would also recommend talking to Energy Star and getting your home rated.http://www.dsireusa.org/library/includes/map2.cfm?CurrentPageID=1&State=MA&RE=1&EE=1http://www.energystar.gov/index.cfm?c=products.pr_tax_credits#s6This a cool idea to save hot water cost's. Would be easy to intergrate into new construction.http://gfxtechnology.com/contents.html#selection

        1. skippy | Nov 09, 2008 04:22pm | #4

          If I end up with the open cell do I need a VP?  I currently have unfaced FB with poly plastic as a VB. But I'm getting mold between the FB and the outside OSB.  During the summer the interior space (walk out basement) is much cooler than the outside.

          Will the closed cell eliminate the vapor infiltration from both sides (from outside in summer and inside in winter)?

           

          Thanks

          1. reinvent | Nov 09, 2008 05:08pm | #5

            In a word Yes. But you should try to determine where that moisture is coming from. Is the poly stapled to the studs over the FG? If so the moisture may be coming up the wall from the basement in which case you should also foam the rim joist.
            BTW open cell foam can be a VB if you paint it.Show us some pics.

            Edited 11/9/2008 9:28 am ET by reinvent

          2. skippy | Nov 10, 2008 02:46am | #6

            The poly is stapled to the exterior studs.

            I plan on covering with 1/2" drywall and then painting that.  I assume that would contribute to providing a VB.

            I'll take some pictures next weekend.

            Thanks

          3. DickRussell | Nov 10, 2008 04:05pm | #7

            Something isn't clear here. You mentioned "walkout basement." Is the mold problem at stid walls built up against concrete foundation walls? If so, the problem is the poly vapor barrier. The concrete will be a source of water vapor all year round, and what you have described (FG batt between studs, covered with VB), is to be avoided.But are you talking about mold in exterior walls above the foundation level?Edit: OK, rereading, I see "mold between the FB and the outside OSB." That suggests moisture getting into the wall cavity at times when the outside is cold. The source could be any of a great number of things, such as moist inside air leaking around the VB (under walls, through electrical outlets, etc), leaks from improperly flashed windows or lack of properly installed and detailed housewrap or tarpaper under the siding. Yeah, find the moisture source first before thinking about how to stuff the cavity with insulation.2nd edit: I just connected this thread with the earlier one from the OP (#112472). Clears up a few things.Edited 11/10/2008 8:11 am ET by DickRussell

            Edited 11/10/2008 8:55 am ET by DickRussell

          4. skippy | Nov 11, 2008 12:12am | #8

            Yeah- the problem is in the studded walls above the foundation.

            I have determined that the moisture is not coming from the outside.

            During the summer the inside temps are as much as 20 degrees cooler.  should I just get rid of that poly plastic VB that's on the inside?

            Skippy

          5. DickRussell | Nov 11, 2008 12:49am | #9

            If inside temperature is cooler than the dew point of the hot, humid summer air, then you can get condensation on the face of the poly VB against the insulation. The wood in the wall will soak up the water. When conditions outside change, you have humid air within the cavity, and possible condensation against the OSB sheathing. However, this doesn't explain why you have mold against the OSB and not on the studs, if I understand your observations correctly.The Building Science site and others have often stated that in all but the coldest climate zones the use of poly VB and vinyl plastic wallpaper inside should be avoided, in favor of a low-perm vapor retarder. This will allow moisture within the cavity that gets in during unusual events to diffuse to the interior and permit drying.There still is the matter of other possible water sources. Others have suggested the still-young concrete foundation losing water, or even wicking it up from the ground. Was the foundation "damp proofed" properly? Are there any cracks in the concrete through which ground water can soak into the concrete itself?

          6. skippy | Nov 13, 2008 09:24pm | #10

            I will take some pictures this weekend and post. The walls sit on a small-what I would call- frost wall. The foundation is a four foot below grade wall-it's like a garage almost.
            Thanks
            Skippy

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