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...

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