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Old 11-21-2012, 09:25 PM   #1
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General cellulose question for the experts!


I have been reading an awful lot about cellulose insulation, and there seems to be some confusion as to how everything works. Watched videos, read many web pages and so on. I have never personally used cellulose, hence my questions here.

It seems that cellulose when installed using the dense pack method is claimed to be an effective air barrier. This claim seems to come from either the installers or the manufacturers. Others seem to disagree saying that without some other form of barrier the cellulose will not be an effective air barrier on it's own. This obviously applies to wall cavities and not ceilings.

What say you?

Now, as far as blowing cellulose into attic spaces, two things appear to be obvious, at least to me. Firstly, it is difficult to get an even thickness and secondly, because of the loose fill nature of the product, there would seem to be any number of cavities which could conceivably leave open spaces for heat to escape.

Educate me please on how these items are addressed. Thanks.

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Old 11-22-2012, 09:32 AM   #2
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i don't see cellulose as being an air barrier. unless you "pack" it solid in there.

in my experience, yes, an "even" layer is difficult. though i am sure pros have the experience to make it pretty even. but it doesn't have to be even, just get it reasonably close. blow enough and you will be good.

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Old 11-22-2012, 09:35 AM   #3
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oh. the "nooks and crannies" . blown cellulose has a talent for getting into everything.
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Old 11-22-2012, 11:21 AM   #4
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Originally Posted by Fix'n it View Post
i don't see cellulose as being an air barrier. unless you "pack" it solid in there.
Thanks Fix'n it: After I posted this yesterday I was still looking for information on how effective cellulose might be as an air barrier. I prefer getting my information from sources that have some authority behind them, and I finally came up with the information that cellulose will not make an effective air barrier, exactly as you say. Even packed solid - while that does apparently help - it is still not an air barrier say in the form of 6 mil poly for example. I found this by following one of Gary's links.
OTOH it will apparently "skin over" in some circumstances, making it the superior choice for blown in attic insulation over chopped fiberglass.
Thank you for your comment, I do appreciate it.
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Old 11-22-2012, 11:22 AM   #5
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General cellulose question for the experts!


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Originally Posted by Fix'n it View Post
oh. the "nooks and crannies" . blown cellulose has a talent for getting into everything.
Agreed...apparently it will do this better than fiberglass.

Thank you again.
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Old 11-22-2012, 01:31 PM   #6
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General cellulose question for the experts!


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Originally Posted by cocobolo View Post
I have been reading an awful lot about cellulose insulation, and there seems to be some confusion as to how everything works. Watched videos, read many web pages and so on. I have never personally used cellulose, hence my questions here.

It seems that cellulose when installed using the dense pack method is claimed to be an effective air barrier. This claim seems to come from either the installers or the manufacturers. Others seem to disagree saying that without some other form of barrier the cellulose will not be an effective air barrier on it's own. This obviously applies to wall cavities and not ceilings.

What say you?

Now, as far as blowing cellulose into attic spaces, two things appear to be obvious, at least to me. Firstly, it is difficult to get an even thickness and secondly, because of the loose fill nature of the product, there would seem to be any number of cavities which could conceivably leave open spaces for heat to escape.

Educate me please on how these items are addressed. Thanks.
Installed at 4.0 densities it will form an effective air barrier. As effective as installed poly, not quite although we see more gaps in poly barriers around wall penetrations so the cellulose might outperform it on the total walls given the slop detailing around electrical outlets.

As effective as spray foam, no.

Don't ever install cellulose in a non-vented roof design. It does not work well and you will have a nightmare on your hands.

It is near impossible to get an exactly level application of any loose blow insulation but I don't think that really matters. It is about getting it up to a minimum established level (i.e. whatever value you want) and it does fill in void spaces quite well.
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Old 11-22-2012, 01:40 PM   #7
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Installed at 4.0 densities it will form an effective air barrier. As effective as installed poly, not quite although we see more gaps in poly barriers around wall penetrations so the cellulose might outperform it on the total walls given the slop detailing around electrical outlets.

As effective as spray foam, no.

Don't ever install cellulose in a non-vented roof design. It does not work well and you will have a nightmare on your hands.

It is near impossible to get an exactly level application of any loose blow insulation but I don't think that really matters. It is about getting it up to a minimum established level (i.e. whatever value you want) and it does fill in void spaces quite well.
Thank you WoW, Having been in the building game for better than 40 years I have seen just how sloppy some installers can be when it comes to a poly v.b. Done with care and all the right pieces it can - and should - be effective. Thank you for the info on installing in a non-vented attic. Can I get you to expand on why this would be? Not questioning you in any way, I simply don't know. Is cellulose actually wet or damp when it is installed? Thanks. Sorry, I missed a question...editing to add it...can you not only get 4.0 densities in wall cavities? Surely this would not be the case in an open attic. Would that be correct? Thanks once again.
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Old 11-22-2012, 01:44 PM   #8
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General cellulose question for the experts!


I agree with you about the poly vapor barrier. Air tight, it works great and will be much tighter than cellulose that is dense packed.

In a non-vented design you would dense pack it dry.

There are just too many examples of sheathing and structure rotting out with a cellulose insulation schedule to trust it.

It is hygroscopic and will draw water to it.

I know that it is not indicated for humid climates or coastal applications but I have yet to personally observe and issue and we live in a very humid and coastal climate.
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Old 11-22-2012, 01:51 PM   #9
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There are just too many examples of sheathing and structure rotting out with a cellulose insulation schedule to trust it.

It is hygroscopic and will draw water to it.
I think you just said the magic word...hygroscopic. That pretty much explains it to me. Many thanks for that.
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Old 11-22-2012, 04:30 PM   #10
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As you want sources...lol;

convective loops in f.g. at low temps:

sensationalized;http://infrared-energy.com/files/Spe...onProblems.pdf

the testing- and a follow-up one, remember this is a low density (0.5#) blown-in, bonded/cubed fiberglass; http://docserver.nrca.net/technical/401.pdf

In defense, and not found in f.g. batt; https://docs.google.com/viewer?a=v&q...mAAqxY_9UrVORg

Lawsuit against the "Thermacube" type; http://www.homeenergy.org/show/artic...zine/77/id/910

Another summary and testing of cellulose results: http://www.homeenergy.org/show/artic...zine/77/id/910

Unbonded blown-in f.g. and the big spread of air-permeability ratings for different densities, pp18, table 2; http://www.ornl.gov/info/reports/1994/3445603820925.pdf Use this (conversion calculator) to convert the density; http://www.unitconversion.org/densit...onversion.html

Interesting read; http://jen.sagepub.com/content/26/2/153.abstract

Cellulose thermal properties testing; http://www.osti.gov/bridge/servlets/...ble/390620.pdf (long time to download)

Material B- 9.4 (0.58# f.g.); http://web.byv.kth.se/bphys/reykjavik/pdf/art_085.pdf

The density of an insulation sets its air permeability. https://docs.google.com/viewer?a=v&q...M8l_EeA2F-qvvA

Cellulose is blown in attics at 1.5# density while f.g. is around 0.55#; http://ws680.nist.gov/bees/ProductLi...Fiberglass.pdf
not much mass there... http://docs.google.com/viewer?a=v&q=...Sl4MDm_aao1YUg

How about adding more blown-in f.g. to stop the convective loops, or 2" of cellulose? https://docs.google.com/viewer?a=v&q...SWhJRhM2V4M5EQ

Moisture; Blown Insulation after all - quick q's (I think)

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Old 11-22-2012, 04:53 PM   #11
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Gary, as always, you are an absolute gold mine of information. So yet again, thank you most sincerely.
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Old 11-22-2012, 05:37 PM   #12
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LOL. To all members: the white "search box" at the top of every page will bring a multitude of posts on the subject entered; eg.- "cellulose insulation in attic" gives: http://www.diychatroom.com/search.php?searchid=3612201

Though it usually doesn't answer the more technical questions, at least not with the latest answers... I do get carried away on certain subjects, lol.

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Old 11-23-2012, 08:19 AM   #13
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what is 4.0 densities ?

when i said "pack it in there". i mean, to the point that it will hold a shape while standing on its own.
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Old 11-23-2012, 01:09 PM   #14
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what is 4.0 densities ?
I believe that refers to the weight per cubic foot once it is packed. In this case,4 pounds per cubic foot. Installed loose it is far less.
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Old 11-23-2012, 01:46 PM   #15
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This is interesting, I see why you wanted to know about the insulation now.

"I have spent the past several weeks trying to design a small net zero energy house and the v.b. and thermal bridging are two of the most important aspects of such a design."

I hope you post about your small zero energy house that will be really interesting. I use to read the "Mother Earth News" for all of the great information about so many subjects, one being insulation and different ways to build an energy efficient home. One question you asked earlier about the cellulose, it is wet when blown in the walls. My insulation subs would spray a 1/2 of foam on all the exterior walls for a vapor barrier, then the cellulose. If you want a great sound barrier around the bathrooms, cellulose is fantastic as a sound killer.

Gary, now I never will get through reading.

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