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  1. #1

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    Default Help Needed - Open Cell vs Closed Cell Spray Foam Insulation?

    I am in the process of insulating my attic and was wondering which type of sprayed foam insulation is better to use. The home is in metro Atlanta, GA. The winters can and do get pretty cold (below freezing); the summers are very hot (currently 96 degrees F).

    I've read various articles from websites that seem to have a bias of one or the other. Closed cell seems to be the most popular, yet more expensive product.

    However, I would like to hear from some fellow Polkies about which way to go.

    I am going to have the underside of the roof sprayed. The shingles are seal tab shingles on the roof.

    Any advice would be greatly appreciated.

    P.S.: If any Polkies provide these services, let me know.
    Last edited by toucanet; 07-30-2010 at 04:42 PM.
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  2. #2

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    The insulation subcontractor that our company uses came back from a convention in Las Vegas with nightmare tales of spray foam.

    He said the biggest concern for people that live in a home being treated is the high level of outgasing that occurs for weeks after the primary application. There are some very nasty toxins in that material and it's not something you would want your family breathing if you can avoid it.

    Alternately once the foam "sets" natural expansion and contraction of the roof framing can cause gaps to appear thus reducing the overall efficiency of teh treatment.

    For these and other reasons we tend to suggest blown cellulose for beefing up attic insulation. It's fairly inert and depending on what you have it usually only takes a few more inches of depth to get your ceiling up to R 50.

    As for your actual question concerning open or closed cell I can't say because I have no first hand experience, but I would definitely ask your contractor about these other issues as well.
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    The last house I built we did a Hybrid system in the ceiling. We sprayed the closed cell foam @ 1"-2" thick after the drywall was installed and then sprayed @ 14" of the white cellulose which makes for a really tight seal and the owner has commented on how quiet and seemingly efficient the house is for its size.

    In fact I was at the house today to paint an accent color in a niche and it is a very quiet house and the only way I could hear cars driving by was through the fireplace flue which is slightly open for a gas fireplace.

    Scott
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  4. #4

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    I don't think you're supposed to insulate the actual roof? I think you should have good ceiling insulation in the attic.
    To reduce cooling costs in the summer, you might want to install some exhaust fans in the roof, powered, with 1 leg broken through a temperature switch set to 80*F+, that way, it'll only come on and exhaust the hot air when the space temp reaches a certain set point. Thus reducing heat transfer between the attic and the cooled spaces below.
    This would not be any benefit for heating, but, again, ceiling isulation, and a programmable thermostat.
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  5. #5

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    Quote Originally Posted by MillerLiteScott View Post
    The last house I built we did a Hybrid system in the ceiling. We sprayed the closed cell foam @ 1"-2" thick after the drywall was installed and then sprayed @ 14" of the white cellulose which makes for a really tight seal and the owner has commented on how quiet and seemingly efficient the house is for its size.

    In fact I was at the house today to paint an accent color in a niche and it is a very quiet house and the only way I could hear cars driving by was through the fireplace flue which is slightly open for a gas fireplace.

    Scott
    That's interesting. I never considered that there might be an added "sound" advantage to the spray. Did you treat the walls in a similar fashion? Dense pack or bat?

    Sorry if I'm side tracking the point here
    Baby Einstein has never sounded so good.

  6. #6

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    Quote Originally Posted by Rev. Hayes View Post
    The insulation subcontractor that our company uses came back from a convention in Las Vegas with nightmare tales of spray foam.

    He said the biggest concern for people that live in a home being treated is the high level of outgasing that occurs for weeks after the primary application. There are some very nasty toxins in that material and it's not something you would want your family breathing if you can avoid it.

    Alternately once the foam "sets" natural expansion and contraction of the roof framing can cause gaps to appear thus reducing the overall efficiency of teh treatment.

    For these and other reasons we tend to suggest blown cellulose for beefing up attic insulation. It's fairly inert and depending on what you have it usually only takes a few more inches of depth to get your ceiling up to R 50.

    As for your actual question concerning open or closed cell I can't say because I have no first hand experience, but I would definitely ask your contractor about these other issues as well.
    I read about the off-gassing and will plan to stay elsewhere for one week while the home is properly vented.

    The open cell insulation has an elasticity factor that I do not know. The closed cell is very dense, with no flexibility.

    As for the blown cellulose, what benefits will that provide for my HVAC unit that is in the attic compared to spraying the underside of the roof? There seems to be some type of substrate that is fastened to the underside of the roof (plywood) with the insulation being sprayed onto this substrate.
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  7. #7

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    Don't know if this information is helpful or not, but I'm in the business of selling products with these two kinds of foams - but I'm no chemical engineer either if there's some on here.

    Open cell means it has tiny holes within each small air-cell (air pocket) within the foam, allowing air or water to enter each cell. It allows it to expand and contract - when physical pressure applied - to a much further degree and "breathes" more than closed cell. Sink sponges, your mattress top and car seats cushions are all examples of this foam.

    Closed cell means each air-cell is closed - no air or water able to penetrate. It is usually stiff and hard compared to the other type. The cheap, orange life-jackets used for boating have this stiff foam inside of them.

    Don't know what would be good for insulation, but might be educational. One thing I would ask, is to see if the foam that they spray has any formaldehyde in it? It is used in curing some foams, and not supposed to be very healthy to breathe.

    Good luck!
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  8. #8

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    A radiant barrier may be an alternative to spraying the underside of the roof. Use the money you saved to add insulation to the attic floor.

    http://www.atticfoil.com/

  9. #9

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    You need to provide a vent/air space between the roof sheathing and the foam layer or you'll "cook" your shingles! There's a formed foam panel thats made for this, it looks kinda like a takeout box from a restaurant. I am getting a high density foam sprayed on the exterior of my 200 yr. old log house in a 2" thickness for a R value of 11-12. If your rafters/trusses aren't going to be touched much, I'd go with the cheaper composite blown-on stuff. This is similar to blown-in loose fill except it's shot with a glue/binder stuff to make it stick where it's shot. Easy to clean up whereas polyfoam AIN'T!;)

  10. #10

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    As has been said, you want the insulation at your ceiling, not on the other side of the attic space, against the Roof framing. As has been said, you want your Roof to be able to 'breath'. Once you are 'clear' on that, +1 on the system Miller LIte recommended, spray foam to seal everything up and then either cellose or fiberglass blown in insulation will get you the best system for the $$. IMHO.

    PS: I have never heard of uing 'open-cell' foam, at least not in the NW.

  11. #11

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    Typical down here is radiant barrier on the roof, blown cellulose in the attic and fiberglass bats or foam in the walls. I did quite a bit of research on foam insulation when I was considering building my own house and I have walked some new construction that was using foam and none had it in the attics or underside of the roof.

    The only homes that I can think of that are using closed cell foam, in some applications, are SIP homes.
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