|
Central Kansas | Closed Cell: 2 lbs per cu. ft; R-value 6 per inch after aging; semi-impermeable to vapor; it is an air barrier; the blowing agent is a hydrofluorocarbon.
Open Cell: 1/2 lb per cu. ft.; R-value 3.5 per inch, is permeable to vapor; it is an air barrier; the blowing agent is water.
Closed cell foam's greater density, 2 lbs vs. 1/2 lb., increases its R-value and offers it the rigidity that open-cell lacks. Tests have confirmed that closed cell can actually increase the shear strength of conventionally framed walls by 30% (Nat'l. Assoc. of Home Builders). Closed cell also has a low vapor-permeability rating and is considered a class-II vapor retarder, meaning it is semi-permeable.
Open-cell foam (Icynene and Demilec) has a greater expansion rate than closed-cell foam. It expands 100 times its initial volume while closed cell expands only 30 times...so less foam is needed to insulate a house. Although both foams will dry if they ever get wet, open cell foam is vapor permeable and dries much faster than closed-cell foam.
Open cell's one major weakness is its lower R-value, roughly 3.5 per inch. This means that when used in a 2x4 exterior wall, it will create an assembly that's approximately only R-12, which won't meet code in most parts of the country.
===> As you know, R-40 walls and R-60 roof are not an accurate reflection of overall thermal performance. Open-cell foam reaches a point of diminishing return at around 5" of thickness and that threshold is even lower with closed cell foam.....which starts at about 3-4". Each additional inch of either foam adds little to the performance. The air barrier and lack of infiltration is the primary advantage of foam insulation...not the stacked up R value you can attain.
Keep in mind that the fear associated with foam insulation carries over from the 70's when urea-formaldehye insulation was used. It would degrade and off-gass unsafe formaldehyde. Current foams are very safe...but protection from the petroleum-based isocyanate is necessary. The second part contains a catalyst, polyol resin, a surfactant, and a blowing agent. Over 3 months to a year, part of the blowing agent in closed-cell is lost to the atmosphere. Prior to 2003, they damaged the atmosphere and maybe people...but since then, the hydrofluorocarbon (HFC) has been deemed safe. During this off-gas period, closed cell will lose R-value.
I built a house in 2003, used Icynene in ceiling, walls, and below frost line in crawl space. Centeral Kansas. 45 gal. of propane per month for the last 3 years in the winter.....2300 sq. ft., 1 level. Works great....tough to hear outside noise however.
| |
|
Lets talk insulation . . spray foams and blown types ~
