Are cellulose manufacturers coverage charts accurate?
My name is Todd Witt and I own Synergy Home Performance LLC in Decatur, AL. We install spray foam insulation, encapsulate crawlspaces, perform HVAC design services and energy audit and home evaluations. I grew up working in the cellulose industry and my father founded Cell-Pak Insulation. The last time I looked at a Cell-Pak coverage chart for R30 insulation it was around 28 sf per bag. I have noticed a new cellulose company, Carolina Fibers, quoting 34.4 sf per bag for an R30. Cellulose seems to be all the rage for the editors of Green Building Advisor. I would love to see a true field installation with these crazy coverage numbers and see how far off they are. Unscrupulous manufacturers have always gotten away with unrealistic coverage charts and it is time they get shut down!
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Replies
How heavy are the bags? Are they even the same volume?
The objective metric is pounds per cubic foot.
It seems to me it wouldn’t be too difficult to test this: no special equipment is really needed. Frame a simple box a foot deep with some scrap plywood or whatever you have handy. Hang some poly around it so that no material is lost during “installation”. Get a bag, rent a blower, and apply the cellulose to your box of known dimensions. If you make your box 6 feet square and 1 foot deep, 36 cubic feet is a full fill, or 36 square feet (since it’s a foot deep, the math is easy :-)
Measure the depth you get and see how far a bag goes. If you get close to spec, then the manufacturer is honest. If you get something WAY off, then the manufacturers numbers are suspect.
Bill
I like this answer!
My son and I recently blew the attic in his garage on a home he purchased this last summer.
Bought the cellulose and rented the blower from local big box lumber supply.
The math was easy and perhaps we did not adjust the equipment properly however we felt ripped of and needed to go back and buy a LOT more to complete our little 22*22 foot attic.
Greenfiber or Insulmax by chance?
Certain brands are compacted denser for packaging/shipping and while it may be theoretically possible to achieve the square footage the reality is the machines don't shred and fluff it enough prior to going into the airlock so your installing at a higher density and lose yield.
Not to mention they are filled with plastic and other garbage.
I use a regional producer, coverage charts are very accurate. Same weight bags and if you put one side by side with a box store bag you’ll see how much larger the premium bags since they aren't as compressed.
I just did my attic with Greenfiber, and I probably would have needed 15-20% more than their chart says to hit the R value I was going for (R60). But I decided it was good enough as is (around R50), and I was too exhausted to go back to the store for more bags.
I added cellulose over old blown in fiberglass, and the depth wasn't consistent across the attic, so that was a bit of an unknown. I also suspect their calculator doesn't fully account for the fiberglass compressing under the weight of the cellulose.
Coverage charts are usually predicated on specific settings with particular blowers, and may not match what a beat up single stage rental blower with the leaking seals delivers.
I've yet to see a coverage chart that looked like a blatant lie though.