Section 5.5.3/Opaque Envelope Insulation Requirements
ASHRAE 90.1 Section 5.5.3 establishes minimum insulation R-values and maximum U-factors for opaque envelope assemblies by climate zone.
Opaque building envelope assemblies (roofs, walls, floors, below-grade walls, slab-on-grade floors) must meet the insulation and U-factor requirements in Tables 5.5-1 through 5.5-8 for the applicable climate zone. The tables provide either minimum R-values for insulation alone or maximum U-factors for the entire assembly. Continuous insulation (ci) requirements are specified separately from cavity insulation. Metal building assemblies, steel-framed, wood-framed, and mass walls each have their own table with different requirements.
Why this section exists
The opaque envelope is responsible for the majority of heating and cooling energy transfer through the building skin. Insulation requirements are calibrated by climate zone because heating-dominated climates need more insulation to retain heat while cooling-dominated climates need less insulation but better solar control. The separate tables for each construction type account for the different thermal bridging characteristics of steel framing, wood framing, and mass walls.
What plan reviewers look for
Plan reviewers check wall sections, roof details, and floor assemblies for insulation types and R-values. They verify that the values meet the applicable table for the climate zone and construction type. They pay particular attention to continuous insulation requirements, which must be uninterrupted by framing, and to the distinction between above-grade and below-grade wall requirements.
Common violations
Related ASHRAE 90.1 requirements
Section 5.5.4 covers fenestration requirements. Section 5.4.3 covers air barrier requirements. Section 5.8 covers the building envelope trade-off option (COMcheck). The IECC Section C402 provides equivalent prescriptive requirements.