IECC includes two different tables - one that identifies the required R-value for insulation, and one that identifies the required U-factor for the total wall. Applicable Internationally. Either approach can be used to satisfy the prerequisite. For ICFs and SIPs, the prerequisite can only be met using added insulation, as per the Rating System: "alternative wall and insulation systems, such as SIPs and ICFs, must demonstrate a comparable R-value, but thermal mass or infiltration effects cannot be included in the R-value calculation. Applicable Internationally.