C503.3.1 Roof replacement. Roof replacements shall comply with Section C402.1.3, C402.1.4, C402.1.5 or C407 where the existing roof assembly is part of the building thermal envelope and contains insulation entirely above the roof deck.
Existing buildings requirements are sprinkled throughout the I-Codes; for roofing replacements it is necessary to look at the IBC (International Building Code), the IEBC (International Existing Building Code), and the IECC (International Energy Conservation Code). The IBC addresses weather protection, fire resistance, and structural performance requirements, while the IEBC includes provisions for retrofit upgrades under certain conditions.
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.