04-27-11, 06:32 AM | #10 | |
Journeyman EcoRenovator
Join Date: May 2009
Location: Buffalo, NY
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Quote:
Foam is rated based on its "stabilized R-Value". The R-value drops over the first two years or so, but then plateaus after all the bubbles that are going to collapse have done so. The R-value would be higher than advertized during the first two years. Of course, fiberglass and cellulose settle and lose R-value over time too, so it's smart to compare aged to aged. Unlike fibrous insulations, the R-value of foam is not affected by wind. It forms a very durable barrier to air and vapor. The fact that it repels water while cellulose absorbs it seems more like a bonus than a drawback. They do burn energetically, but they contain fire retardants, and meet fire code when installed behind drywall. Good enough for me. And yes, in the event of a structure fire, I'll pop on a charcoal respirator. Different blowing agents are available. The used to use CFC's. R134a is one option, which is ironic considering its GWP. Other foams use various inerts, including CO2. To tell a contractor to spray foam, without specifying a specific foam and friendly blowing agent, would be crazy. However, whether adequate performance can be derived from, say, a CO2-blown foam remains to be seen. The Rth of air at STP is about R-5.5 per inch, so that's the best you can do with tiny bubbles of immobile air. |
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