Posted By Bob I on 07 Nov 2013 01:03 PM
confused? scammed would be a better term. insulation doesn't settle that much.
Back in the late 1980s to mid-1990s "fluffing" blown insultation with too low a density was pretty common. Haven't heard much lately- I suspect the fly-by-nighters have long since gone out of business.
If you deal with an established insulation contractor there will be a track record and a reputation.
Fluffed fiberglass doesn't tend to settle in attic blows- it just hangs there under-performing for years/decades. Fluffed cellulose can settle quite a bit (and quickly) due it's density.
The settling rate and total settling of cellulose is a function of the amount of seasonal moisture cycling in/out of the cellulose occurs. The ultimate settled density is climate-dependent, and sometimes house-specific, but for open blow goods it would rarely exceed 2lbs per cubic foot unless you literally soaked it, more than once. If you care enough about it, take a square foot of the installed cellulose (at a representative average depth), scoop it into a bag and weigh it, you'd be able to tell how much it might have been fluffed. Initial installed density if done legit would be about 1.3-1.4 lbs per cubic foot, settled density in the 1.40-1.5ish range.
If it was an overblow on R11 batts the fiberglass would sink to about 3" under the weight and be good for about R10, so to hit R38 you'd need R28 of cellulose, which would be about 8" of cellulose initial blow, settling to about 7.5". That's 2/3 of a cubic foot per square foot of area, so if blown at proper density your square-foot sample should weigh about a pound. If it has settled to 2" of cellulose would be a very crusty & dense 5-6lbs per cubic foot papier-mache' brick!