Energy · IECC 2021 §R403.3.3
Ducts Buried in Attic Insulation
Ducts buried in ceiling insulation: R-8 duct insulation, R-19 of ceiling insulation above plus below the duct, fully buried R-13 supply ducts in zones 0A to 3A, and the 3 ft supply outlet exception.. Referenced to IECC 2021 §R403.3.3.
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