Blown Cellulose vs. Blown Fiberglass?
Last Post 19 May 2022 02:37 PM by sailawayrb. 10 Replies.
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JohnRLeeUser is Offline
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17 Jan 2017 08:29 PM
I requested blown cellulose (R38) from my insulation contractor and that is what he bid.  Now that drywall is installed, it will be soon time to insulate the attic.

I first want to air seal the ceiling deck...around cans, and other cracks that might exist...before having him blow in the R38 insulation.  I plan on using a latex roof elastomeric compound and some 3M 8067 tape that I have left over to seal any areas needed.

Insulation contractor is suggesting I use blown fiberglass instead.  It is cheaper and he added it doesn't "settle" like cellulose (this is a vented attic - vented soffits to a vented roof ridge cap).  Someone also suggested less mold issues with fiberglass than cellulose.

This is Northern Cal coastal property, Trinidad - 95570, high humidity but dew points that are typically too low to create mold issues (typically)

I imagine I will spend time over the years in the attic.  I built a cat walk that runs the entire length of the attic so I will not need to trample the insulation and derelict the R value. 

I hate fiberglass, blown cellulose is much more friendly to the lungs and skin.  It is used frequently these days.  Should I even consider fiberglass? Even if the cellulose settles over the next 10 years, I can always blow in a few more inches myself, if that time comes?

As always, your comments are welcome.
NashvegasUser is Offline
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17 Jan 2017 09:17 PM
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NashvegasUser is Offline
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17 Jan 2017 09:18 PM
I may be at odds with others on the forum, but I have used blown fiberglass (Owens Corning) several times for attic and walls. I have been pleased with it. It has a very low irritablity especially compared to standards batts. I have seen cellulose in an attic totally deteriorated and nothing more than a powder. That was my reason for going to fiberglass. The only thing that I recall is Dana1 indicates that fiberglass is more transparent to infrared, but shouldnt be an issue in your location.
arkie6User is Offline
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18 Jan 2017 12:50 AM
Have you considered stabilized cellulose?

http://greenbuildingtalk.com/Forums...fault.aspx
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18 Jan 2017 05:26 PM
Posted By arkie6 on 18 Jan 2017 12:50 AM
Have you considered stabilized cellulose?

http://greenbuildingtalk.com/Forums...fault.aspx

I assumed they would use stabilized cellulose.  Most of the white fluff I see in attics around Kansas has moisture integrated into it to keep dust down.  I assume that is "stabilized".  From what I've read, most cellulose blown these days is some form of stabilized?  Due to the dust from completely dry cellulose, not being able to see what or where you're blowing.

However, it seems the Applegate products may be a bit more unique?  It is stabilized with borate solution moisture, for fire retardants purposes and they also had some sort of adhesive to keep it from sagging and drifting? I would also think the borate would keep mold from growing and insects from being attracted to the cellulose (termites?)
arkie6User is Offline
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19 Jan 2017 07:52 AM
Dry blown cellulose in attics is the norm in my area. Very few insulation installers in my area use stabilized cellulose in the attic.  Dry blown cellulose typically contains a combination of borates and sulfates and is lower cost than borate only cellulose used in stabilized cellulose.  The sulfates don't play well with water.
smartwallUser is Offline
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19 Jan 2017 08:21 AM
Stabilized refers to non sulfate cellulose. All borax fire proofing would be a stabilized product. The homearammas in my area sell sulfate based cellulose which when moisture is added turns to acid as per your high school chemistry. Hence the action called sublimation, which turns the paper into dust over time. Fiberglass is a stable product the only precaution I would give is that it can be over blown. You need an accurate bag count for the sq ft that you cover. The first time I installed Insulsafe we had our machine settings for cellulose and ended up blowing a 24" depth for a R-19 cap. All manufacturers have all borate products and they're only a couple of bucks more for a 30 lb bag.
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17 Mar 2017 06:38 AM
All things being equal & everything being done properly (air sealing, baffles, hatches) - both work fine but cellulose will win out not because of your reasons, but the simple fact that FG R-Value drops the hotter it gets.

Granted you could argue that if it was as dense as cellulose, the convection issue would be diminished but it would not be eliminated & said convection issue is one of the biggest causes of FG's loss of R-Value. Of course once both products are saturated with heat (for better lack of a term) the game is over and it is up to the AC unit to work it's magic

As an FYI, many FG manufacturers are using recycled materials to make the product & in either case recycled doesn't always mean better - some methods & the means required to make a product from recycled materials can use more energy & put off more by products than simply using new materials
newbostonconstUser is Offline
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17 Mar 2017 10:50 AM
Summary of points:
Cellulose is 3.65 times the weight of fiberglass for same R value.
Cellulose blocks wind penetration.
Cellulose holds IR heat in better
Cellulose R per inch 3.7 compare to 3 for fiberglass
Cellulose better sound blocking
"Never argue with an idiot. They will only bring you down to their level and beat you with experience." George Carlins
ArshineFeedUser is Offline
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19 May 2022 05:51 AM
Have you considered stabilized cellulose?
https://www.arshinefeed.com/
sailawayrbUser is Offline
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19 May 2022 02:37 PM
See Smartwall's comment with regard to stabilized cellulose.

We greatly prefer blown fiberglass for attics. It is way lighter and doesn't settle nearly as much. Fiberglass makes it affordable and easy to create long life R70+ attics. This blown in fiberglass also does not have the health issues like the stuff they used in years past. You should still wear a proper mask when installing it though.
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