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Q.The federal stimulus plan’s energy tax credits for insulation are based on the 2009 IECC, which raises the wall insulation requirement for climate zones 5 and 6 from R-19 to R-20. To meet this requirement, the R-value of the cavity insulation must be at least 3.63 per inch. Does this mean that standard R-19 fiberglass batts used to insulate 2x6 walls would not qualify for the tax credit? How about Icynene, an open-cell spray foam with an R-value of 3.6 per inch?

A.Martin Holladay, senior editor at GreenBuilding Advisor.com, responds: Since insulation lobbyists were closely involved with this code change, it should come as no surprise to learn that manufacturers of fiberglass batts, open-cell spray foam, and cellulose insulation can all provide products meeting the new requirement.

Most builders complied with the old code by compressing 6-inch-thick R-19 fiberglass batts into 5 1/2-inch-thick wall cavities. Since the batts are labeled “R-19,” most inspectors accepted the practice, even though the actual R-value of these compressed batts is only R-18. But fiberglass manufacturers have long produced 51/2-inch-thick high-density R-21 batts that fit a 2x6 wall without compression. More expensive than R-19 batts, these high-density batts will meet the new code, but because they aren’t typically stocked by most insulation contractors, home centers, or lumberyards, they will probably have to be special-ordered.

According to a spokesperson, Icynene has recently reformulated its open-cell spray foam to increase its R-value from 3.6 to 3.7 per inch, in anticipation of the code change. Now a 51/2-inch wall insulated with Icynene can claim an R-value of 20.35. With a higher density than open-cell foam and an R-value exceeding 6 per inch, closed-cell polyurethane foam has no problem meeting the new code.

The R-value of cellulose insulation depends on its density. Denser installations of cellulose have lower levels of air infiltration (but also a lower R-value per inch) than fluffier installations. When installed using the dense-pack method (about 3.5 pounds per cubic foot density), cellulose achieves R-3.65 per inch, suitable for meeting the new IECC.