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Open cell vs Cellulose

BobHr | Posted in General Questions on

In retrofitting walls how does open cell and dense pack compare for air tightness?

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Replies

  1. Riversong | | #1

    That's a pretty narrow basis for comparison.

    Spray foam, if installed properly - the right mix, the right rate, the right substrate temperature - will always be somewhat more air-tight than any fibrous insulation. But dense-pack cellulose does a better job at reducing air movement than any other fibrous insulation because of its exceptionally high density. It has been third-party certified as a fire stop because of this and its fire-resistant quality.

    For instance J CHESNUT (12/23/2010) reported here that "My CFM @ 50 Pasc was reduced from 2,925 to 1,625. I did some minor air sealing around the house but this is mostly due to dense packing the balloon framed walls with cellulose."

    But cellulose offers so many additional advantages with none of the disadvantages of petrochemical foam, such as off-gassing, possible shrinkage or separation from shrinking framing, and fire and toxic smoke contribution.

    Cellulose is highly fire-resistant, insect & rodent resistant, mold resistant, non-toxic to humans and pets, excellent sound dampener, 100% recycled, very low ecological footprint, recyclable and compostable, and has a higher R per inch than open cell.

    Additionally, it's hygroscopic qualities allows it to buffer indoor relative humidity, absorb and release up to 30 times its weight in moisture, draws moisture away from wood framing and thus protecting it, and allows the house to breathe.

    It's also less expensive, no one has to vacate the house or wear a hazmat suit during installation, and it makes renovations or mechanical system repairs much easier.

  2. GBA Editor
    Martin Holladay | | #2

    Robert,
    The best data on this issue were collected by researcher Bruce Harley. I reported on his findings in the April 2005 issue of Energy Design Update.

    Harley reviewed blower door test results from 906 recently build New England homes, and sorted the data by insulation type. The data clearly showed that homes insulated with cellulose (average air leakage, 0.31 ACHnat) were tighter than homes insulated with fiberglass batts (average air leakage, 0.38 ACHnat), and homes insulated with spray foam (0.26 ACHnat) were tighter than homes insulated with cellulose.

    Here are some excerpts from the article:
    "Recently Bruce Harley, the technical director for residential energy services for the Conservation Services Group in Westborough, Massachusetts, was able to study correlations between airtightness and insulation type in a much larger number of buildings. Harley assembled airtightness data on Energy Star homes (including single-family and multifamily homes) completed in 2004 in Massachusetts and Rhode Island. All of the homes were blower-door tested after completion.

    "...Harley found that houses with walls insulated with spray polyurethane foam were significantly tighter than those houses with walls insulated with cellulose, and that houses with walls insulated with cellulose were significantly tighter than those insulated with fiberglass...

    "Although the data clearly show a consistent correlation between insulation type and airtightness, the reasons for the correlation are unknown. It is possible that builders who choose cellulose or spray foam insulation — both of which have a reputation for resisting air flow — may be more meticulous in performing air sealing tasks than builders who choose fiberglass batts. Perhaps builders’ attention to detail in certain areas unrelated to insulation performance — for example, careful sealing between wall bottom plates and subfloors — partially explains the measured differences in airtightness. If this theory is true, the extra dedication to air sealing may be motivated by the builders’ desire to justify the added cost of spray foam or cellulose over fiberglass batts.

    "However, the principle of Occam’s Razor favors a simpler explanation: that the measured differences in airtightness are due to differences in the material characteristics of the different insulations."

  3. Allan Edwards | | #3

    Martin

    Thanks for the information, I assume I can find a link on that article. Do you know if there are any shrinkage issues with open cell foam. Regarding the off-gassing, I've seen a few complaints from homeowners who used open cell foam in existing homes but haven't seen much evidence in new homes. Do you have any information on this?

    Allan

  4. GBA Editor
    Martin Holladay | | #4

    Allan,
    I didn't think the EDU article was available on the Web -- most issues of EDU aren't -- but I did a search and you're in luck. It is posted here:
    http://www.aspenpublishers.com/PDF/SS07413629.pdf

    The article I referred to starts on page 10.

    All of the cases of spray-foam shrinkage that I have heard about arose because of problems with the chemicals being mixed, bad mixing ratios, or installation in cold conditions.

    JLC published a great article by Mason Knowles on spray foam problems, and it's posted on the Web. Check it out: Troubleshooting Spray-Foam Insulation.

    You're right that most of the well-publicized examples of spray foam outgassing complaints come from foam sprayed in occupied existing homes. However, the issue is still being investigated and I think that it's too early to draw firm conclusions on the extent of the problem.

  5. Don Purington | | #5

    Allan,

    Here is a link to the April 2005 issue of Energy Design Update containing Bruce Harley's article titled "Fiberglass-Insulated Homes Are the Leakiest" on pages 10-11.

    http://www.aspenpublishers.com/PDF/SS07413629.pdf

    Don

  6. Allan Edwards | | #6

    Thanks Martin (and Don). I am headed to NAHB show today in Orlando and plan to quiz the Icynene folks about some of these issues. I know, the manufacturers are going to spin everything to their advantage but I like to hear both sides. I’ll have my iPad with me and plan to show them a few GBA forum posts about their product (especially Robert’s).

    Allan

  7. J99aAMQzYo | | #7

    For "air tightness", ocSPF wins every time ... IF "perfectly" installed by a highly skilled installer, etc., etc. etc.

    For known carcinogens, bio-accumulating mutagens, multiple-chemical sensitivity initiators/aggravators, lethal cyanide fire-smoke development, etc., etc., etc. ... ocSPF also wins every time.

    Not a contest I'm interested in "winning" in the spaces in which we spend the greatest majority of our lives just to save 0.05 ACHnat.

  8. Riversong | | #8

    Andy,

    That's well put.

    Martin,

    I think it's a bit disingenuous and misleading to claim a significant difference between 0.26 and 0.31 ACHnat. That's probably within the margin of error, and it compares averages which can be skewed by the extreme ends of the curves rather than medians. It also fails to compare houses that are entirely insulated with one insulation type, separating wall insulation from ceiling insulation. So it's not clear from the article how useful or accurate the conclusions are.

    My last dense-pack ADA house tested at 0.10 ACHnat (0.15 with the air inlets open), and that's a significant reduction in air flow from any of the Harley average numbers.

    I stand by my statement that spray foam will be somewhat more air tight than dense-pack.

  9. GBA Editor
    Martin Holladay | | #9

    Robert,
    I was presenting the best data I am aware of.

    The data are in fact significant -- not only because of the differences in air leakage rates shown, but because of the consistency of the correlation. Bruce tried looking at various subsets of the measured houses and each subset showed the same consistent correlation.

    So the results are significant from a statistical standpoint. The results demonstrate a correlation.

    That said, you can, of course, build an extremely tight house that is insulated with cellulose.

  10. Riversong | | #10

    you can, of course, build an extremely tight house that is insulted with cellulose.

    Freudian slip?

  11. Riversong | | #11

    the results are significant from a statistical standpoint

    Paraphrased from Wikipedia:

    In statistics, a result is called statistically significant if it is unlikely to have occurred by chance. As used in statistics, significant does not mean important or meaningful, as it does in everyday speech. The result may be statistically significant, but the difference may be small enough to be utterly unimportant. Many researchers urge that tests of significance should always be accompanied by effect-size statistics, which approximate the size and thus the practical importance of the difference.

  12. GBA Editor
    Martin Holladay | | #12

    For lack of a nail, the shoe was lost. For lack of an "a," my meaning was changed.

  13. Robert Hronek | | #13

    Several months ago, I am not sure I have the name right, Mr.Susz posted a comment about his experiences with blower doors tests. He said he would post results of his tests but I never saw a follow up. His original comment led me to believe the cellulose was very close to achiving the same results.

    What I am interested in is retrofiting existing walls. Retrofit presents challenges that are different than working in an open wall. Install foam though a tube is different than spraying. So I would like apple to apple reuslts.

  14. GBA Editor
    Martin Holladay | | #14

    Robert,
    If you are planning to insulate existing walls, use cellulose.

  15. user-788447 | | #15

    Robert,
    Drill and fill installers of dens pac cellulose gain a feel of how well the material is being packed by pressure on the tubes.
    I wonder how a foam installer gauges how good of a job they are doing in progress? As you are likely aware you can't tell how well a job they did unless it is inspected afterward with a blower door/ infrared cam inspection.

    Its a bit of a hit and miss operation. Not only is cellulose non-toxic with far less overall environmental impact it is probably more forgiving if the installers need to come back and fill missed spots if found.

  16. Riversong | | #16

    Robert H,

    If you're thinking about installing foam through a tube, then you're talking tripolymer or air-krete.

  17. Robert Hronek | | #17

    We are working on getting started in energy retrofits. Our idea is to install cellulose and not foam.

    In talking with a local foam installer at a home show he talked about installing foam with a fill tube. I also ran across a home had retrofit wall foam, found it when I had a return air grill off.

    the guy at the home show described it as open cell. If this is not open cell then how does it compare?

  18. WildBunchFarm | | #18

    I know the last post from this thread was 5 years ago, but I didn't want to start a new one since my question relates to the topic.

    I recently got an insulation quote back and the Icynene open cell foam will be cheaper than dense packed cellulose (Greenfiber brand). The difference is not inconsequential either as it will be $1,925 less to go with the Icynene. This was surprising to me.

    I am still reluctant to go with the Icynene because of the concerns with potential voids in my 10" thick walls and potential smell. But with the price difference being that great - it sure it tempting.

    Here were the final numbers
    For 2400 square feet of 10" thick walls
    Icynene = $3,975
    Dense packed cellulose with netting = $5900

    For my basement walls - I'm going with Icynene closed cell spray foam as it doesn't look like there is a better alternative.

  19. GBA Editor
    Martin Holladay | | #19

    Jimmy,
    It looks like you forgot to include your question.

  20. Expert Member
    Dana Dorsett | | #20

    It's common to find open cell coming in cheaper than dense-packing in netting.

    2400 square feet x 10" depth is 24,000 board-feet (2000 cubic feet). A price of 24,000 board-feet of open cell foam for $4000 comes under 17 cents per board foot, which is literally HALF what I've become accustomed to seeing. Could it be a misquote? It would have to be installed in two lifts, with a cooling off period long enough to allow the curing heat of the first pass to dissipate fully.

    2000 cubic feet of 3.5lb cellulose is 7000 lbs of material. Even at wholesale that's going to be more than 2 grand in just material cost, and the installation labor is higher than with open cell foam. That much dense packed cellulose has a measurable thermal mass benefit too.

    Icynene's water blown 2lb foam (MD-R-200 or MD-R-210) are greener alternatives to their MD-C-200 closed cell foam, which is blown with HFC245fa.

  21. Chaubenee | | #21

    After being convinced by solid reasoning and data and the proponents of dense pack (such as Dana) , I sought out to find a qualified installer of the product for my house. I did find him and we are using that product in my 2x6walls and attic. I am using some open cell in places where it behooves me and that would be in the corners, above the mud sill and above the upper plate on top of the accuvents, and in the joist bays between the first and second floors. In every stud bay, and between all 2x members like plates and jacks, we are installing elastomeric caulking to increase air tightness. I imagine the tightness will be magnificent with the dense pack and the air sealing measures. I don't think you can just blow in cellulose and be happy with the results if you did not focus some effort and time into air sealing methods. I think there is a place for some open cell foam in a building these days, but doing the entire building is overkill in my opinion.

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