Section C402.2/Specific Insulation Requirements
IECC C402.2 provides prescriptive minimum insulation R-values and maximum assembly U-factors for roofs, walls, floors, and slabs by climate zone.
Section C402.2 requires specific insulation levels for each opaque envelope component based on climate zone. Roofs (C402.2.1) must meet insulation requirements based on whether the insulation is entirely above the deck, in the attic, or within a metal building. Above-grade walls (C402.2.2) are separated into mass walls, metal building walls, steel-framed walls, and wood-framed/other walls, each with different R-value or U-factor requirements. Below-grade walls (C402.2.3) require insulation to a specified depth. Floors (C402.2.4) must meet requirements based on framing type, with separate values for mass floors, steel-joist floors, and wood-framed floors. Slab-on-grade perimeter insulation (C402.2.5) is required in climate zones 4 and above for unheated slabs and in climate zones 1 and above for heated slabs. All prescriptive values are found in Tables C402.1.3 and C402.1.4.
Why this section exists
The building envelope is responsible for the majority of heating and cooling energy use in commercial buildings. Inadequate insulation increases energy consumption, operating costs, and carbon emissions for the life of the building. The climate-zone-based requirements ensure insulation levels are calibrated to local heating and cooling demands. Separate requirements for different assembly types (mass, steel-framed, wood-framed) account for the thermal bridging characteristics of each construction method. Steel framing, for example, requires higher R-values because the highly conductive steel studs create significant thermal bridges that reduce the effective R-value of the assembly.
What plan reviewers look for
Plan reviewers check wall sections, roof details, and foundation details for insulation type, thickness, and R-value. They verify the project's climate zone and confirm insulation values match the prescriptive tables. They check for continuous insulation (ci) where required, verifying it is shown on the exterior side of the framing without breaks at structural members. They verify slab edge insulation depth and R-value in climate zones where it is required. For the air leakage requirements that work alongside insulation, they check Section C402.1 for the overall envelope compliance path.