How many inches of blown in FG in a ceiling does it take to get R-30?
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That depends on how it is installled.
For a cathedral cieling where it is stuffed for dense-packed ( BIBBS) where the convection is nearly eliminated, ten or eleven inches will do the job. It is rated I think at about 3.4R so that fits a 2x12 with a flovent if you choose to use one.
But in a typical flat cieling where it ends up fluffy, my guy installs fifteen inches deep. He says that uses the same amt ( Pounds) of the chopped FG as eleven inches packed densely. The looser fill allows convection currents thru it.
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The looser fill allows convection currents thru it.
Reducing it to an effective R nothing?
Joe H
That's what the cellulose giuys argue.My experience is that it is better than batts by far and customers are satisfied. The instaler just says that it takes the greater depth to get the same R-value.Remember there was a similar arguement over cells in walls, that they will settle and leave gap or allow convection lose unless packed tight enough so it is measured in pounds installed? Or in cileings, it eventually settles to self pack for greater density. The FG settles in to the cieling too.
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P, if it isn't DPed into the walls properly it will settle and leave a gap at the top. I've seen it happen in less than 6 months.
Like anything else, if it's not done right, it isn't right.
As to settlement in the ceiling or attic I don't think air will move through the cells the way it passes through FG.
"I don't think" isn't the same as I'm positive, but the gaps in FG are much larger than with cells.
Joe H
You may be righter, especially for attics
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Well, technically, same as in a batt--about 9-10".
In reality, telling the installer to aim for 12" will likely get you close enough.
Unless you are getting a really, really, really, great deal on either the FG or the install (or both), cellulose is so much nicer to work with. Especially in the "fussy" areas like soffit vents, can lights, fan boxes, bathroom & kitchen vents and the like, where you have to wade in and work by hand to do it right. But, that's a personal observation garnered from personal experience, too.
"cellulose is so much nicer to work with. "HUnh????!!I'll make a bed in chopped FG before I want to get anywhere near cellulose fibres! And we get the chopped FG for only about six to eight cents a foot more than the cells.
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I want to get anywhere near cellulose fibres!
Could be I'm waxing nostalgic, it's happened before--can't remember the last time that there was only one kind of fiber to work in, really. Mix fg, cellulose, rock wool, and that amalgam of "attic stuff" that's part deck grains, part duct insualtion, part dust, part I-don't-wann-know . . . and none of it is much fun <sigh>. I swear some days, it'd be easier to jsut use a chipper and blow straw & nettles in . . .
I know my skin reacts much more strongly to FG than anything else; so that might bias me, too.Occupational hazard of my occupation not being around (sorry Bubba)
Mine too with batt FG, but have you handled or seen the chopped FG for blowing? It is more like cotton balls
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