Blown in cellulose, fiberglass, or batts for attic?

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I want to upgrade my attic insulation. I have 2x6 beams and old unfaced R13-R19 fiberglass batts up there. I want to add R38 on top of the existing insulation. I am in San Jose, CA.
I can do cellulose, which will give me uniform coverage and is the least expensive option. But I've heard it's very dusty (even after it's done, my furnace hot air ducts runs in the attic), not easy to deal with if I need to go up the attic and do something, and boric acid/ink may give off bad VOC.
I can do blown-in fiberglass, but how do I ensure the contractor won't fluff the insulation? I am also not fond of the idea of lose fiberglass floating around in the attic. They may get sucked into the furnace duct and gets into the house.
I can do fiberglass rolls. Less chance of lose fiber floating around, and R38 is R38. But it may not insulate as well as blown-in since it's layed on top of my existing insulation and the coverage won't be as uniform as blown-in. But advantage is I can move it out if I need to go up and do something.
I am leaning toward the 3rd option. Assume the contractor does a decent job, will it provide adequate insulation? Between a reasonably installed (ie, average, not perfect) batt vs blown-in cellulose, how does the fiberglass batt compare? If it's 80% as good, then I think I am fine with it...
Thanks!
Raymond
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I would go for the cellulose. It tends to seal better. As for the dust, that is only a problem if you are up there or if you have leaky returns. The supply side will not pull any dust in and frankly if there is nothing to move the stuff, I don't see there being a dust problem, once it is in.

... am fine with it...

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If he has it blown in there with a water spray (ie: stabilized blow) it won't move and it won't settle.
s

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how about closed cell expanding foam ? R6 per inch.
pricey but great insulator
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I thought there was all kinds of controversary about that stuff. Moisture wicking, offgassing, etc. Or am i thinking of another product?
s (not to mention, you'd never pull a wire through it) LOL!

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I went for the batts. It is great to be able to move them aside to add a wire or whatever. I did it myself. It probably took 3-4 hours.
As far as insulation value, if you place them carefully together, fiberglass should be fine. And it doesn't settle over time like the blown in cellulose I put in my previous house.
Bob
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wrote:

[cut]
Why aren't you considering icynene or polyurethane for maximum insulation?
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Because it would cost way more for the same insulation level, It's difficult to install also. Foams only make sense for me if there is not space enough for conventional insulations. Also, it would make re-working things in the space very difficult.
Bob
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They cost more than cellulose or fiberglass, and installing the stuff on top of existing non-rigid insulation is silly.
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Chris Lewis,

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a. cellulose is the best option. b. how could the fiberglass get 'sucked' into the furnace ducts? do you have an open return air vent in your attic? c. cellulose is the best option
www.centralfiber.com for some good reading.
steve

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It's to your advantage to have the insulation fluffed. Because the dead air space is what does the insulating.
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Christopher A. Young
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< snipped-for-privacy@none.com> wrote in message
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On Nov 1, 4:23 pm, snipped-for-privacy@none.com wrote:

Ray-
fiberglass rolls at 90 deg to current rolls...keep clear of roof underside & allow for eave to ridge venting Any gaps between the layersis just more dead air space...free insulation.
btw are you adding R-19 to get up to R-38 total or adding R-38?
San Jose is a pretty mild climate so R-38 total should be plenty.
I'm in Orange County & I put R-30 in 1980; fiberglass rolls that I just rolled back to do some attic work :)
The R-30 works pretty good for me but the old house is not as tight as it could be due to other issues.
IMO blow-in cellulose is good stuff, it works but its a mess if you ever need to revisit the attic. I hate it!
My parent's house has blow-in cellulose & it's been keeping the place warm for ~30 years.
cheers Bob
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Thanks everyone for the reply!

Ok I will keep that in mind and make sure the contractor does this.

I am adding R38 on top of existing stuff, which is probably R13.

The contractor said the cost difference between R38 and R30 is minimal compare to the cost of the job, so I am just going to go max and install R38.
Thanks!
Raymond
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Ask your contractor if he can do rockwool (eg: Roxul).
Generally it's the same price as fiberglass, but is slightly superior in all respects. Particularly that it's a lot less picky and less likely to blow around. Can be blown or used as batts.
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Can you elaborate on why it's slightly superior? Thanks!
Raymond
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I'm speaking of Roxul here, I'm not familiar with other brands. The Roxul product is manufactured under license from a European company IIRC, and is somewhat different than the (much older) forms of rock wool I've encountered.
Roxul is quite popular in Canada and I believe it's becoming more popular in the US.
The R value is slightly higher than fiberglass (R21.5 vs R20 I think for 5.5" batts).
It's heavier, and is a better sound barrier.
The fibers are larger and heavier, doesn't "fly" as much during installation (no clouds of fine particles), and isn't so "picky". Eg: you won't be breathing the stuff nor itching for days nor finding it stuck/embedded in everything. Easier to cut. It's much more pleasant to work with.
[As long as you're not working overhead, it's reasonable to install rockwool without gloves/skin/breathing/eye protection.]
Even fiberglass will sog/permanently pack down to a certain extent with moisture. Rock wool won't pack down, and sheds water quicker.
While fiberglass isn't flammable, the binders are, and the stuff melts fairly readily. Rockwool has no binders, and the melt point is considerably higher. Rockwool is thus considerably more fire resistant than fiberglass.
Here (Roxul is big in Canada), the price per square foot is usually identical to fiberglass. Most people who try Roxul won't go back to fiberglass. We had roof insulation upgraded with blown in (shredded batts) Roxul, and there was virtually _no_ dust anywhere, and I wouldn't think of using anything else. I've also helped insulate a church extension (about 500 square feet) with batts, and it was much nicer than previous fiberglass jobs.
About the only drawback to rockwool is that it doesn't compress as much as fiberglass, so your order will consume more shipping/ storage space.
I have no relationship to the Roxul company, other than as a satisfied customer ;-)
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Chris Lewis,

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Sounds good. About the weight, I have standard 1/2" ceiling sheetrock. Will the weight be an issue? If I go with batts, it will be resting on the wood beams which should be fine, but if I go with blown-in, then the weight might rest on the ceiling. Just don't want a sagged ceiling, not to mention this is an earthquake area. Ho much heavier is it compare to fiberglass and cellulose?
If I go with blown-in, how difficult will it be to move them aside to do some work? I like the fire resistent and moisture resistent property.
Thanks!
Raymond
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No. It's still mostly air ;-)

Roxul is spun mining slag, fiberglass is spun glass. Slag is slighty heavier than glass, and the fibers are fatter, but it's still mostly air. A roxul batt is probably less than 50% heavier than a fiberglass batt.

You just push it out of the way. Because of its higher weight and fiber size it won't produce a vast cloud of flying fibers like fiberglass does.
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Chris Lewis,

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On Nov 6, 8:40 am, snipped-for-privacy@nortelnetworks.com (Chris Lewis) wrote:

Roxul's Rock Wool Insulation MSDS, available on their Web site, contradicts this, saying that it contains one to six percent "Cured Urea Extended Phenolic Formaldehyde Binder." The binder undergoes "thermal decomposition" above 200 degrees Celsius, releasing the usual suspects as gases. "Acrid smoke may be generated during a fire."
<http://www.roxul.com/graphics/RX-NA/Canada/products/Roxul%20Material %20Safety%20Data%20Sheet%2004-1-071.pdf>
--Eric Smith
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Odd. I have done simplistic burn tests of both fiberglass and Roxul - "try to light with a lighter". Fiberglass burns briefly, gives off smoke, and melts. The Roxul glowed red, and that's all it did. I've seen a video of a similar test with a propane torch with similar results, and Roxul's fire resistance over fiberglass is touted as one of the advantages.
Tho, the latter could be it slows down fire spread in building structures, not that it doesn't emit something in a fire.
Formulation change? Different product? Brain damage?
Dunno ;-)
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Chris Lewis,

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