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  1. #1

    Open vs. Closed cell blown foam insulation

    I live in the Dallas area and my builder is asking whether we want open cell or closed cell blown foam insulation. He suggests open cell because it allows the home to breathe more, thereby reducing moisture and mold problems.

    Does anyone have an opinion on open cell versus closed cell? Thanks.

  2. #2
    Join Date
    Aug 2006
    Location
    Utah
    Posts
    23
    I am building a home and I have done a LOT of research on this issue. After all of that research the choice is very clear - closed cell all the way.

    Icynene is the leading open cell foam and has been marketed masterfully. However, they have created so much confusion that many home builders think they have to use open cell because "it allows the home to breathe" or "if the roof leaks you can see the leak." That is all baloney.

    I recommend that you go to this forum and read what some of the people there are saying. http://www.sprayfoam.com/mnps/boards...ys=0&startat=1

    One caution - the insulation will not mean much if you get some hack to do the HVAC job. Make sure that you find someone that does heat load calculations on every home. Someone that believes in Manual J, D, and S. If they size the HVAC system using some rule of thumb, run away as fast as you can. You will find as I have that there are very few HVAC guys that do the heat load calcs and/or actually believe in Manual J, D, and S.

  3. #3
    Join Date
    Jul 2007
    Posts
    8
    Quote Originally Posted by dblagent007 View Post
    One caution - the insulation will not mean much if you get some hack to do the HVAC job. Make sure that you find someone that does heat load calculations on every home. Someone that believes in Manual J, D, and S. If they size the HVAC system using some rule of thumb, run away as fast as you can. You will find as I have that there are very few HVAC guys that do the heat load calcs and/or actually believe in Manual J, D, and S.
    I second, third and fourth that. I have called all around my area, and there are only 2 who will do the calculations, but they won't do it without charging me a fee for "checking my system first". If you are having trouble finding a contractor who will do Manual J, D and S, go to http://www.acca.org

    Insist that the builder use a contractor who will properly size your system. Ask for the paperwork showing their calculations. You'll be happier in the long run.

  4. #4
    Join Date
    Aug 2006
    Location
    Utah
    Posts
    23
    Quote Originally Posted by my5sons View Post
    I second, third and fourth that. I have called all around my area, and there are only 2 who will do the calculations, but they won't do it without charging me a fee for "checking my system first". If you are having trouble finding a contractor who will do Manual J, D and S, go to http://www.acca.org

    Insist that the builder use a contractor who will properly size your system. Ask for the paperwork showing their calculations. You'll be happier in the long run.
    I found that lots of them will do the calcs if you ask. However, they don't really believe the calcs because they always say "I can do the calcs, but it will be just about the same size as it would be using my rule of thumb." Stay away from these people. Find the ones that do the calcs because they believe it is necessary to properly size the system. Do not use the ones that do the calcs only as an afterthought to verify their rule of thumb because I can guarantee you that if the calcs and the rule of thumb are different they will go with the rule of thumb.

  5. #5
    Join Date
    Jul 2007
    Posts
    8
    Quote Originally Posted by dblagent007 View Post
    I found that lots of them will do the calcs if you ask. However, they don't really believe the calcs because they always say "I can do the calcs, but it will be just about the same size as it would be using my rule of thumb." Stay away from these people. Find the ones that do the calcs because they believe it is necessary to properly size the system. Do not use the ones that do the calcs only as an afterthought to verify their rule of thumb because I can guarantee you that if the calcs and the rule of thumb are different they will go with the rule of thumb.
    Yes, very true, and I also read that some of the ones doing the Manual J calculations are padding it with an additional 25% as a rule of thumb, which severly oversizes the system. How do you know if they are using only Manual J?

  6. #6
    Join Date
    Nov 2006
    Location
    TEXAS
    Posts
    806
    I'm in the process of designing the specs for my home using spray foam. I'm thinking about using .5# open cell in the walls and 2# closed cell in the roof to create a semi conditioned area where my HVAC system and ducts will live. You'll also want some fresh air intake and a reliable way to exhaust stale bathroom and kitchen air. Make sure the HVAC co. that does the work considers the superior insulation and need for moisture control and doesn't oversize. I'd like to see a variable speed two stage system with options for humidity control.
    Avatar is a tribute to my Great Grandfather, Andrew Stewart. This pin was one of his advertisements for his heating and plumbing business. I never knew him but must of inherited his love of things mechanical since I am the only blue collar worker in the family

  7. #7
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,599
    Good insulation and being air tight is excellent. The final touch is to provide make-up air ventilation and humidity control during low a/c load. You need 50-75 cfm of fresh filtered air when the home is occupied. This purges indoor pollutants and renews oxygen. The ideal comfort level is <50%RH. These humidity levels also prevent mold and dust mites. During wet cool weather, the moisture load in the fresh air may be 2-3 lbs. per hour. Add the minor internal moisture loads from people & activities could be another lb./hour. Suggest a whole house ventilating dehumidifier that removes 3-4 lbs. of moisture per hour. These units are able to blend/distribute fresh filtered air throughout the home when needed. Also they maintain <50%RH throughout any a/c operation. Dehu TB

  8. #8
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    respitory doctors recomment = 55% < RH > 35%

    one must check the shrinkage value of sprayed foam -- say after 5y.

    one must consider the toxicity in case of a fire --

    Icyene seems to be good.

    check the R values
    harvest rainwater,make SHADE,R75/50/30= roof/wall/floor, use HVAC mastic,caulk all wall seams!

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