attic insulation...cellulose ir fiberglass ?

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  #1  
Old 04-11-08, 12:13 PM
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attic insulation...cellulose ir fiberglass ?

what are the pro's & con's..?
between blown in cellulose.
and blown in fiberglass.

any information would be great
 
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Old 04-11-08, 01:05 PM
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Let's see, from memory:

FG doesn't maintain it's R-value as temps drop, air can wash through it negating its insulation value.

Cellulose maintains its R-value, doesn't let air wash through it, settles in and fills hard to insulate crevices, and the settling helps seal air leaks.
 
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Old 04-11-08, 03:47 PM
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Ah, but...over time cellulose compacts and loses R value, plus it's dusty. You have to leave the area over the soffit vents uncovered...if you use cellulose, install the styro baffles to keep the fill from clogging the vents.Also, depends on whether you're installing yourself- I think fiberglass is easier.

Connie
 
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Old 04-11-08, 04:23 PM
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attic insulation...cellulose ir fiberglass ?

You have to install baffles with any bulk insulation. The process is the same except there may be a bigger problem with inhalation of the glass fibers.

Fiberglass batts may be easier if you want to take your time by using batts. The problem with batts is the gaps and difficulty filling around truss members, especially if you lay a second layer perpendicular to the trusses or framing members.

Technically, there may be a slight loss of R-value if there is settlement, but the decreased air infiltrationoff sets that. Unfortunately, the archaic and simplistic "pink" R-value concept of measuring insulating ability does not include real factors like infiltration and credits for weight.
 
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Old 04-11-08, 04:30 PM
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Oh, Dick, I didn't know you're supposed to put baffles with fiberglass. I stapled the paper to the joists for the first layer, while I held it back from the eaves, then just crossed the second layer loose. Think that's OK? I know it's not blocking the vents, and it's been up there about 10 years
 
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Old 04-11-08, 05:12 PM
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attic insulation...cellulose ir fiberglass ?

Connie -

The original post was asking the difference between BLOWN fibergalss and cellulose. - If you have paper and are stapleing, you have BATT insulation and not BLOWN.

You also apparently were laying additional BATTS perpendicular to the first and the the roof framing, so you obviously encountered the openings around the trusses or braces. Just another reason for going with blown.

Remember, the advertised R-value is a lab test based on a pure surface of the insulation over a short period of time, so it does not include the time lag that heavier materials provide and does not include the loss for the thermal short-circuiting of the wood or steel. That is the reason an R19 batt in a wall will give a real wall R-value of R11 to R17 depending on the spacing and material in the framing members without factoring in the air infiltration loss.
 
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Old 04-11-08, 08:01 PM
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Ok, thanks...I got it (even if I did nod off once or twice

For some reason, when I read your reply, I thought you said baffles for either type...I think if you visit too many threads at a time it makes you logy.
 
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