Section C402.1/Building Envelope Requirements
IECC C402.1 establishes thermal envelope performance requirements including insulation R-values, fenestration U-factors, and air barrier continuity.
The building thermal envelope must comply with the prescriptive insulation and fenestration requirements of Tables C402.1.3 and C402.4, or demonstrate compliance through one of the alternative paths (total building performance per C407 or energy cost budget per C406). Opaque envelope assemblies must meet or exceed the minimum R-values (or maximum U-factors) for the climate zone. A continuous air barrier must be provided throughout the building envelope.
Why this section exists
The building envelope is the primary barrier between conditioned interior space and the outdoor environment. An inadequately insulated or leaky envelope increases heating and cooling energy consumption, creates comfort problems (drafts, cold surfaces), and can lead to condensation and moisture damage. The prescriptive requirements establish minimum performance levels based on the climate zone severity.
What plan reviewers look for
Plan reviewers check wall sections, roof assemblies, and floor details for insulation types and R-values. They verify that the specified values meet Table C402.1.3 for the project's climate zone. They check the fenestration schedule for U-factors and solar heat gain coefficients (SHGC). They also look for air barrier continuity details at transitions between wall, roof, and foundation assemblies.
Common violations
Related IECC requirements
Section C402.2 covers specific roof insulation requirements. Section C402.4 covers fenestration. Section C403 covers mechanical system efficiency. ASHRAE 90.1 provides an alternative compliance path that is referenced by the IECC.