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Old 11-03-2011, 05:11 PM   #1
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Attic Insulation: Should I use fiberglass or cellulose?


I need to add some attic insulation and after researching and asking questions I'm just as confused as I was before I started.

I currently have some cellulose (blown-in) up there. I had my ceiling/attic penetrations sealed up with spray foam last spring and the contractor told me that I have R-29 now and recommends putting another R-30 of blown-in fiberglass. They also said it's not a difficult diy job if I want to do it myself to save some money.

The buildingscience page seems to say that fiberglass isn't as effective as cellulose because of it's lower density. A google search yields a lot of similar information attesting to this.

When I went to the home improvement store, the cost difference between cellulose and fiberglass is substantial. But it also appears a lot easier and faster to blow in.

Would there be any reason for me to choose cellulose over fiberglass other than price? Considering I already have cellulose up there and I've had my attic floor sealed is performance going to be much different? The fiberglass I'm looking at is OC's attic cat.

Thanks.

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Old 11-03-2011, 06:15 PM   #2
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Attic Insulation: Should I use fiberglass or cellulose?


Cellulose is much better.

Borate only stabilized cellulose at that.

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Old 11-03-2011, 08:25 PM   #3
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Attic Insulation: Should I use fiberglass or cellulose?


+1.... The real question is, is there any reason whatsoever for you to use fiberglass in your application? The answer is no. Cellulose is less costly, will offer superior performance, and you already have an existing layer... Seems like a no-brainer.
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Old 11-03-2011, 11:57 PM   #4
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Attic Insulation: Should I use fiberglass or cellulose?


Long as your drywall/span can handle the added weight: http://www.energyguide.com/library/E...SubjectID=8375

http://michaelbluejay.com/electricity/insulation.html

http://www.cellulose.org/userdocs/Te...ectiveness.pdf

http://docs.google.com/viewer?a=v&q=...MrFpuTdu1ubwtA

Or f.g, though I'm not a big fan: The "biggest loser" in fiberglass insulation....

Check for your Code required minimum, per location: http://publicecodes.citation.com/ico...001_par001.htm

http://publicecodes.citation.com/ico..._11_sec002.htm

Because.........http://www.buildings.com/ArticleDeta...1/Default.aspx

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Old 11-04-2011, 01:35 AM   #5
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Attic Insulation: Should I use fiberglass or cellulose?


Good info GBR.

Is there a simple way to determine my drywall thickness/span so I can see how much more weight my ceiling can tolerate?
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Old 11-04-2011, 05:08 PM   #6
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Attic Insulation: Should I use fiberglass or cellulose?


” regular drywall, 24”o.c.--------1.6#,

5/8” board, 24” o.c.-------2.2#,

” at 16”o.c.---- 2.2#,

Table #4, page #9: http://gypsum.org/pdf/GA-216-2010.html

Check at the attic access (scuttle-hole) edge. Look in the attic to see spacing of the ceiling joists.


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Old 11-04-2011, 11:03 PM   #7
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Attic Insulation: Should I use fiberglass or cellulose?


There is a roof vent on both peaks of the house. There is NO insulation in the soffit area along the base of the attic floor. I am going to put pink rolled batting over the existing old blown in. My question? should I put the pink in the soffit areas???l Oh I am a woman age 63 and love to do it myself. I know to remove the paper off the pink batts for the added insulation. IF I have to put in the soffit area do I remove the paper?? Thanks in advance for any and all help. Did the crawlspace floors over the summer, pink down, paper up against the floor!!!
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Old 11-05-2011, 10:31 AM   #8
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Attic Insulation: Should I use fiberglass or cellulose?


Do not put insulation in the soffit area or you will block the intake of air into the attic. The peak vents are where the air goes out...the soffit is where the air comes in, provided you have soffit vents, that is.
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Old 11-05-2011, 11:37 AM   #9
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Attic Insulation: Should I use fiberglass or cellulose?


Correct, I agree. Good that you know to remove the facing (if over existing b.i.) or the blown-in and reinstall it over the faced batts. You should add baffles to direct the air up the roof sheathing away from the insulation to degrade it's R-value (and the edge of the f.g. batt). http://www.bergerbuildingproducts.co...sAccuvent.html

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Old 11-09-2011, 08:03 AM   #10
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Attic Insulation: Should I use fiberglass or cellulose?


Thank you for your help. Insulated the attic above the bathroom, pantry and kitchen yesterday. High winds today and colder. Sounds silly to say, but rooms already feel warmer. Bath and Pantry hit directly from the Northside and No wind block. Thanks Again! Carol
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Old 11-09-2011, 07:42 PM   #11
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Attic Insulation: Should I use fiberglass or cellulose?


Quote:
Originally Posted by Windows on Wash View Post
Cellulose is much better.

Borate only stabilized cellulose at that.
Why? If cellulose gets wet, it compacts and basically turns to mud. It also loses the fire-resistance after it dries out. So it's useless and a fire hazard. Fiberglass doesn't absorb water, and if it gets wet, can be "fluffed" after it dries.

Can you explain why it's "much better"?

R-30 is R-30 regardless of what is doing the insulation, yes? No?
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Old 11-10-2011, 08:50 AM   #12
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Attic Insulation: Should I use fiberglass or cellulose?


From a company standpoint, cellulose is much safer for my installers and the residents if they need to get into the attic.

From a performance standpoint, cellulose has a much higher density and therefore does not suffer for the convective looping issue that fiberglass does and the resultant loss of R-Value.

If you have a 20 degree temperature differential from attic to inside living space, blown in fiberglass will only perform at roughly 60% of its indicated R-value once you factor in the convective air looping and striped R-value.

example:
10" of blown in fiberglass is (for the sake of argument) and R30
10" of cellulose is also and R30

20 degree difference makes the fiberglass perform at R18 whereas the cellulose is holding steady at an R30.

I don't think you should choose an insulation based on which one is more resistant to water leaks as that is not its intended purpose.
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Old 11-10-2011, 11:15 AM   #13
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Attic Insulation: Should I use fiberglass or cellulose?


Interesting... definitely something to think about there.

I understand what you're saying about the blown in, but what about the rolls of batting? Assuming they are cut and fit in correctly of course.

Quote:
I don't think you should choose an insulation based on which one is more resistant to water leaks as that is not its intended purpose.
Well, when you have to consider what would have to be done after a water leak in the attic (certainly not unheard of) I think it does factor in.

If the cellulose gets wet and dries, it is no longer fire resistant, so once it has been wet it needs to be removed. Now, granted, if fiberglass gets wet, you still have to figure out how you're going to get it completely dry; but once it's dry and assuming it's not compacted, it's back to what it was.
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Old 11-10-2011, 08:10 PM   #14
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Attic Insulation: Should I use fiberglass or cellulose?


I would base my decision on insulation on which product does a better job of insulating rather than its performance after being wet.

Batts are fine if you get a high density batt but will require a much more careful installation. Fiberglass is also much more of an inhalation and health hazard.

I will defer to GBRs thorough write up on fiberglass and the comparison.

The "biggest loser" in fiberglass insulation....

The post is pretty unarguable in this case.

Whatever product is damaged after a leak can easily be replaced with what will likely be covered by one bag of cellulose.

When we have seen a cellulose that has gotten wet, it is normally dried out by the time the repairs are completed. You can break it back up once it is dry and cover it with new cellulose.
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Old 11-10-2011, 09:08 PM   #15
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Attic Insulation: Should I use fiberglass or cellulose?


Thanks! I appreciate your time and input (and that is not "said" sarcastically)

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