Another disadvantage of spray foam is the sealing action and complete filling of cavities. If you ever want to renovate, the electric and plumbing runs are sealed in a solid block of foam. It's not impossible to work on the stuff inside the block, but it should be considered as a permanent component that cannot be modified after being sprayed. For this reason, most contractors do not completely fill up wall cavities.
Blown in cellulose insulation is very close in performance to spray foam insulation inside cavities. The difference between the two depends on how stringent your requirements and specs are. Spray foam is absolutely a vapor barrier, where cellulose is somewhat of a vapor barrier. When properly applied, spray foam absolutely does not breathe, or allow any infiltration of air, where cellulose allows a miniscule amount of air and vapor to pass through. With enough pressure applied, cellulose will breathe 50 to 60 percent more air than spray foam. This relates to 0.2 air changes per hour vs 0.3, so 50 percent more than nearly nothing is still almost nearly nothing.
Probably the three most important factors to consider are fire safety, cost, and "eco-greenness". Cellulose is a winner by a landslide in all three categories. Cellulose is classified as a fire retardant material, where spray foam requires a fire barrier around it (because it can burn violently and release toxic vapors). Spray foam costs two to three times the price of cellulose, plus you get a cavity that is not completely filled (which short changes you from some insulating value). On the eco-friendly green factor, cellulose is 85 to 90 percent recycled paper, where spray foam is 100 percent refined petroleum.
|