Ready to get blown

Highbeam Posted By Highbeam, Sep 29, 2010 at 3:45 PM

  1. Highbeam

    Highbeam
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    Reggie: I wasn't trying to convice anybody of which is better. This thread is about the doing of it, not about which material is better. Nobody ever said it was likely to burn, it's paper, make your own decision about that. And yes, it is much like cotton candy, did you listen in chemistry class? Did you even read the thread?

    I'm not buying the loss of half the R-value in cold weather. That's silly.
     
  2. vvvv

    vvvv
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    celluLOSE ? + SUCROSE BURN?
     
  3. Highbeam

    Highbeam
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    It took me a little bit to find some quantitative analysis of this supposed reduction in R-value of blown in fiberglass and cold weather. Well, the facts are that less than a 15% reduction in R-value at 20 degrees F. This of course means your ambient outside temps would need to be much lower than 20 degrees since the attic will always be warmer than ambient outside air. Look at your climate and decide if this amounts to a hill of beans. In the pacific NW it is an insignicant reduction in R-value.

    Cellulose is very heavy too. Not so good with old 1/2" ceiling sheetrock. How do you suppose this chopped up paper handles water? Does it turn into that paper mache' junk from elementary school.

    Have you ever lit a sugar cube on fire?
     
  4. GaryGary

    GaryGary
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    Jul 12, 2010
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    Clearly the decision as to what kind of insulation you want to use is completely up to you and the factors you consider to be important, but the test that shows a reduction in Rvalue of 50% was very carefully run by the National Renewable Energy Lab (NREL) using large attic simulator test rig that was built for this purpose at Oak Ridge.
    The results are here:
    http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/92/920510.html

    It appears to me that the test was very carefully done. I've never seen the results disputed by the FG industry.

    Figure 3 in the report shows the R value going from R19 with a 50F attic temp down to R 9.5 at with an attic temperature of -5F. A reduction of R value by one half for cold conditions. We get temperatures below -5F quite often through the winter.
    If you don't get cold winter temps, maybe its not as much as in issue, but the R value at 25F has already dropped from R19 down to R14 -- about a 25% reduction.

    Gary
     
  5. Highbeam

    Highbeam
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    Bah, that link makes no such conclusions. Very qualitative. The 15% drop at 20 degrees was sourced from the same Oakridge laboratory in another "article". Seems there is no raw data available. So, we can't draw real conclusions with real numbers yet. Just because the ambient air is -5 in MT (Brrr) does not mean that your attic is -5. This is not a problem in most parts of the country so FG will only see a slight reduction in R-value, say 15% at 20 degree attic temp. Mountain out of a molehole I think.
     
  6. Dix

    Dix
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    Well, I finally get to read this thread, and what is my conclusion, you all might ask???


    It needs a different title :coolhmm:



    ;-P
     
  7. GaryGary

    GaryGary
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    Hi,
    I guess you can believe what you will, but I don't see how they could have done the test much more carefully. They built a 14 by 16 ft section of attic with standard home attic construction, they ventilated in the same way that attics are ventilated, and they have temperature control chambers on each side. The figure 3 data is directly from the test -- I would hardly call it qualitative. I've been a engineer for 35 years, with a good deal of experience in setting up and running tests. In my opinion you very rarely find tests done this realistically and this carefully.

    As to -5F, most of the northern tier of states experiences these temperatures, and in the west, all the way down through Colorado. And, the 25% drop in R value for 30F attic temps is hardly insignificant.

    Gary
     
  8. Highbeam

    Highbeam
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    Yeah, that graph had no numbers on the data points. Just a pretty picture. Was there an actual data table somewhere? These types of articles are often biased and especially when there is no data presented.

    Again, you're depending on numbers that are nowhere to be found. I also found an Oakridge data point of 15% drop at 20 degrees attic temp and you found something else. No clear consensus. As an engineer, you should be concerned with both actual data as well as the method by which the data was collected. Show me the data and you might have a point.
     
  9. ISeeDeadBTUs

    ISeeDeadBTUs
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    Speaking of being blown . . .how bout using cellulite for insulation?
     
  10. Highbeam

    Highbeam
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    Guys like gary have actually gotten me second guessing the FG decision. Healthy I suppose. I had a roof leak over the weekend where an area of attic insulation was saturated. What happens to the cellulose stuff when it gets totally wet? The leak was a fart fan roof jack, the roofers attached it with nails that were not covered by the shingles. The exposed (gasketed) nails were enough to let in a lot of water. Enough that I had to poke a hole in my ceiling to drain it. Ugh.

    This was my first time laying in and working in the modern blown FG insulation. It was not itchy. It was like a pile of cotton balls.
     
  11. kenny chaos

    kenny chaos
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    Have you asked any of your local homebuilders or architects what the latest fad is?
    No matter what you do, later you'll wish you did something else.
    That's how that works.
    You've got three pages of ideas. Go ask elsewhere for more, differant, and maybe better, ideas.
     
  12. sesmith

    sesmith
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    My old farmhouse has has foam, fiberglass, and cellulose in it, depending on when the various parts were remodeled. All work, but I can tell you from experience that rodents LOVE fiberglass.Not only that, if they do manage to move into the fiberglass, they trash the insulation. They don't care for foam or cellulose nearly as much. I hate working with fiberglass, so when it recently came to adding more fill to the crawlspace area over much of my house, cellulose won hands down. Easy to work with relatively clean and fairly inexpensive, and not heavy. Any insulation becomes a heavy sloppy mess when wet, but then, my roof doesn't leak (I just replaced that too).
     
  13. GaryGary

    GaryGary
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    Hi Highbeam,

    Maybe we are looking at different articles -- this article:
    http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/92/920510.html

    Has a figure 3 shown here:
    http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/92/920510.html#fig3

    Its a plot of R value vs attic temperature. The vertical axis is the actual measured R value of the insulation, and the horizontal axis is the attic temperature.
    The plotted data points show the R values achieved for the two FG loose fill installations they did.

    For example for the LSCS 1 test run:
    At 50 F attic temp, the first run shows R17.9
    At 28 F attic temp, the R value on the same sample is down to R14
    At -4 F attic temp, the R value on the same sample is down to R9.1

    The data points labeled LSCS 1 and 2 shown in figure 3 are actual measured values from the two separate installations of loose fill FG they did in the test rig attic.

    NREL has no reason to be biased. They are a government operated test organization, and have an excellent reputation -- you can easily verify that with a little Googling.

    Gary
     
  14. mikeyny

    mikeyny
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    thanks for setting things straight Gary, I have been blowing cellulose for many yrs now. I occasionally chime in to give a bit of advice on this subject but sometimes you just can't convince some people how good it really is. Owens Corning has had the market cornered for so long, it's hard to think any other way than pink. If people had any idea how much energy it takes to produce fg compared to cellulose, they would not believe that either. Fiberglass really is a thing of the past.
    Mike
     
  15. woodsmaster

    woodsmaster
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    I would use cellulose if for no other reason than it dosn't make you itch.
     
  16. velvetfoot

    velvetfoot
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  17. Highbeam

    Highbeam
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    Modern fiberglass can be bought in itch-free versions. It's like cotton. No itch. I don't know how they do it.

    I would have to see actual data points for the graph. Show us the numbers. Engineers know that graphs are a way to trick accountants.
     

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