Cellulose or fiberglass insulation?

msroseJuly 10, 2006

We've gotten two estimates so far. The one company uses fiberglass and their estimate was $1,100. The other company uses cellulose and their estimate $764. Is one type of insulation better than the other?


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Both are better; depending upon who you listen to. I built a place in '98; two major concerns of mine were energy efficiency and minimizing environmental impact. Cellulose wins both, hands down in my opinion.

Wive's tale #1 about c'lose . . it has less insulating ability when it's settled. True; however the R-value is based upon SETTLED density . . so you get some "extra" R-value at installation which fades over time to the rated value. If you use wet-blown, no settling occurs.

Wive's tale #2 about c'lose . . it loses it's fire retardancy with time. Horseradish ! I took a sample from a friends house over 20 years old . . could NOT get it to burn in direct propane torch flame. Nor could I get a brand new sample to burn.

Wive's tale #3 about c'lose . . fire retardant is a dangerous chemical. Bolderdash ! Borate salts . . . not terribly far from the stuff used in Borax ( hence it's name ) and also very similar to boric acid used to treat eye infections. While it's not Kool-aid or seasoning; it's certainly not a dangerous chemical unless you purposely ingest the stuff.

It's also a good sound deadener; it was in fact originally developed FOR that purpose.

The very fact that it has a tendancy to settle; is part of what makes it such good insulation . . . tends to move / fill any little gaps etc that occur when the place moves / shrinks / swells throughout the seasons.

I also liked the fact that the embodied energy ( energy used to MAKE the stuff ) is incredibly low when compared to f'glass which takes LOTS of energy to make. No outgassing or "itchies" from cellulose, either. Plus; f'glass will NEVER degrade . . . cellulose eventually will if left to the elements . . .

Perfect stuff for an attic . . . just blow it in, but make SURE you have adequate ventilation up there . . . that applies for ANY insulation . . . .

I'd choose it simply because it's better insulation from any standpoint I know of . . . the fact that in your case it's cheaper is just a bonus . . .

There's my 2 cents . .


    Bookmark   July 10, 2006 at 7:09PM
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Thank you both so much. We had the guys come today and add the cellulose insulation.


    Bookmark   July 13, 2006 at 10:45AM
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One big negative about blown-in cellulose is remodeling projects that require one to re-enter the attic for wiring, bathroom fans, ceiling fans, etc. The stuff is nasty and floats everywhere. I know this from experience. Eye and lung protection are definitely required.

The new plastic faced "soft" fiberglass bats are much more remodel friendly.

So if you go with cellulose, make sure you don't have to go up in the attic again.

    Bookmark   August 2, 2006 at 3:58AM
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I'm told that Cellulose tends to decompose a little after 10-20 years and turn to dust, the borate salts would be in that dust, which forces its way down through cracks and what not.

    Bookmark   August 18, 2006 at 5:22AM
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Cellulose decomposing . . . ever seen an old newspaper ? .. . like really old ? . . . paper is really nothing BUT cellulose. Don't get it wet, no direct sunlight and it lasts FAR longer than you or I will.

Of course borate salts are in the stuff . . . it's supposed to be there. If it's coming down through your ceiling or such; it means you didn't put up a vapor barrier . . a no-no with cellulose or anything else. I'd rather have ( possibly ) newspaper coming down out of my ceiling; than f'glas fibers . . .

Properly done; you'll have nothing coming down; and better insulation . . .


    Bookmark   August 18, 2006 at 6:42AM
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info only .. maybe web tainted, could be right, could be wrong.

Saw a demo at Johns-Manville site of their easy blow-in. Demo'd trouble lights layed on a pile of their fluffy stuff and a pile of cellulose. The cellulose was charred where the bulb touched.

Read somewhere that the typical 75w incandescent A19 bulb is about 450 degrees. Which is some kind of poor mans test for home construction materials fire rating.

Fire departments - They have to break cellulose apart after fires to put out the smoldering as water apparently doesnt penetrate well enough if this insulation is left untouched and the smoldering can later make stuff burst into flames.

Said ; Fiberglass just melts into blobs at somewhere around 225F degrees.

    Bookmark   August 18, 2006 at 11:12AM
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Charring and burning . . . two very different things. I took a sample of cellulose that was going to be blown into my attic . . with propane torch; yeah it turned black and gave off a little smoke. Would NOT burn though . . . repeated test with a 20+ year old sample from a friends house . . same results. You can char a living tree too; doesn't mean it's going to burn.

Smoldering . . . by definition it is burning at an incredibly slow rate . . . cellulose is virtually not combustible, and prevents air infiltration which also helps prevent burning. This hindering of air movement is part of what makes it such good insulation. Smoldering, and perhaps re-kindling a fire later may not be desireable; it's also not a reason to choose an insulation. With smoldering you know that the fire spread slow enough to let all get out safely. I was IN a house fire many moons ago . . have the scars to prove it . . . and cellulose was the hands down choice from every standpoint I used . . . INCLUDING it's performance in fire conditions . . .


    Bookmark   August 18, 2006 at 7:29PM
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Live trees won't burn to a blow torch, but they will burn down in a forest fire. if it will scorch it will probably smolder in the right conditions, so I can see that being a problem, and its imposible to keep something that pulls humidity from the air dry in a humid climate, so I can see it breaking down a little per year (and you only need it to break down a little to get alot more dust than you want) but I aslo see installing vapor barriors and what not as being very helpful to control dust, but Dust falls down wall spaces and out electrical plugs, light switches, and electrical sockets.

    Bookmark   August 19, 2006 at 2:19AM
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I am trying to decide between types of insulation and wanting to avoid chemical out gassing. Installer recommended insulating to R49 (we now have about 6 inches of old fiberglass and this would qualify us for rebate). We have problems with excessive heat in our attic as air flow is low. We have no sidewall vents, no eaves/soffit vents; there is a ridge vent, and two rows of vents on the roof plus an attic fan on the roof and an attic fan in the ceiling. Our furnace has softsided rather than sheetmetal ducts running thru this space,. any recommendations would be appreciated. Quoted $975 for cellulose. (1250 sq ft approx.

    Bookmark   October 18, 2010 at 2:32PM
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