What is the R-value of blown in cellulose at different densities?
Timike2
| Posted in Green Products and Materials on
for a 2×4 wall
1-2 pcf = ? R-value
3-4 pcf =
5-6 pcf =
7-8 pcf =
for a 2×6 wall
1-2 pcf =
3-4 pcf =
5-6 pcf =
7-8 pcf =
What I really want to know is if there is a density where the R-value begins to decrease because it is too dense.
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Blown cellulose in the attic is R3.5-3.70 per inch. Dense packed in wall cavities should only be install at 4psf, and it has a R3.8-3.9 per inch. This is all we spec. I do not know about the performance at other densities.
Tim,
Information from the Cellulose Insulation Manufacturers Association: "In wall applications standard practice is to compact loose-fill cellulose to a density that will prevent settling. While this is a matter of some controversy most authorities recommend a density of at least 3.0 pcf for cellulose insulation in walls. Materials with high nominal settled densities (2.0 pcf and higher) should be installed at 3.5 pcf. Research has confirmed that settling is virtually nil with any cellulose insulation at densities of 3.5 pcf, or higher. Compacting cellulose insulation may produce a very slight reduction of R-value. Specifiers do not need to compensate for settling in attics since federal law (the CPSC standard and the FTC R-Value Rule) requires R-value and coverage data to be stated at settled density. Open blow cellulose installations do lose R-value as the material settles, however such installations provide “bonus R-value” until they reach settled density."
My notes based on interviews with experts: Loose-fill cellulose is R-3.8 per inch and dense-packed cellulose is about 3.65 per inch at a density of 3 1/2 lbs. per cubic foot. Denser than that and the R-value drops off. According to Bohdan Boyko, the fiberized cellulose introduced in 1990 (replacing the earlier hammer-milled cellulose) is about the same R-value per inch whether it is loose-fill or dense-packed. The main advantage of dense packing is not an improvement in R-value; rather, it is a reduction in air infiltration.
Dan Lea has a different take. He tod me, "The guys at ORNL and R&D Services ... [performed] research we paid big bucks to do. Their conclusions: at nominal settled density, cellulose R-value is R-3.6 to R-3.7 per inch; at wall density it is R-3.8 to R-3.9. They base this on studies of multiple materials."
What is the reason for higher density in thick walls? is that purely to reduce settling?
from greenbuildingadvisor.com article How to Install Cellulose Insulation
"When it comes to thick walls, it’s all about density. One thing I have learned over the years is that when we get to thicker walls, we have to increase the density a little more — to just over 4 pounds per cubic foot for a 12-inch thick wall, and to as much as 5.1 pounds per cubic foot for a 27-inch-thick R-100 wall."
The peak R/inch for cellulose occurs somewhere between 2.8 and 3.5lbs in most peoples' testing. At 4lbs and up the R value is definitely falling.
Cellulose settling is largely a function of mechanical creepage from seasonal moisture cycling. Higher density reduces the settling, and for a given amount of moisture cycling there is a density at which it will not settle at all. The characteristics of cellulose insulation and settling has been studied extensively by Torben Valdbjørn Rasmussen in the 1990s and early 2000s in Denmark, with numerous publications detailing the mechanisms, modeling, and experimental verification in the Journal of Building Physics,eg:
http://jen.sagepub.com/content/27/1/49.abstract
The creepage is not affected by the thickness of the walls. Moisture cycling is affected by both climate and construction details, and only do a much lesser degree the R-value/thickness of the assembly. The assertion that it takes 5.1lbs per cubic foot density for 27 inch thick wall of unspecified height, construction and climate should be viewed with some skepticism, given that at 4+ lbs density the R value is definitely falling off. But then, the notion that R100 is a wall-R that would make any design or financial sense is also a bit of a stretch.
There's a plot in ASHRAE fundamentals from about 2.7 pcf up to about 6 pcf. R value per inch goes from about 3.5 at 2.7 pcf down to 3.2 at 6 pdf. Those values are a little lower than what most people report, and they are rough because I'm just estimating off a plot, but the main takeaway is that even if you compress it to an insanely high density, the R-value is still OK--it doesn't suddenly collapse.