The IECC requirement above is limited to those buildings where the roof assembly contains above-deck insulation and is part of the building’s thermal envelope. Roof replacement is a defined term in the I-Codes; the IBC requires removal of the existing roofing materials down to the deck and installing a new roof covering assembly. Under these conditions, the IECC mandates the installation of enough insulation to comply with either the R-Value or U-Factor tables. The use of tapered insulation can help meet the requirement if additional assembly thicknesses are required; the U-Factor approach can provide even more flexibility.

Note that if the roof assembly includes ceiling insulation or below-deck insulation, this requirement does not apply. Additionally, there are other provisions in the IECC that exempt certain roof recovering and roof replacement projects from energy efficiency requirements, depending on the buildings energy use, roof design and other factors.