Wall and Roof U-Factor Calculator (IECC Envelope Check)

Effective R-value and U-factor of wood stud, steel stud, mass and roof assemblies, checked against IECC 2021 / 2024 prescriptive maximums.

Parallel-path method for wood framing, ASHRAE effective R-values for steel studs
Cladding, sheathing, continuous insulation, cavity insulation and interior finish layers
Roofs with insulation above the deck, and attics
Pass/fail against the IECC commercial or residential maximum U-factor for the climate zone
Thickness of continuous insulation needed to comply
Assembly section diagram and layer-by-layer R-values

How to use

Choose the assembly: wood or steel stud wall, mass wall, roof with insulation above the deck, or attic.
Set the framing and the nominal R-value of the cavity insulation (for example R-21 in 2×6 studs).
Add continuous insulation and its thickness, then the cladding, sheathing and interior finish.
Read the assembly U-factor and effective R-value. Steel studs conduct heat, so R-13 between them counts as about R-6.
Pick the climate zone (it starts from the Climate Zone tool), commercial or residential, and the IECC edition to see the maximum U-factor and whether the assembly meets it. If it does not, the tool gives the continuous insulation thickness that would.
Material values are typical published figures. Use tested or listed values for a compliance submission.
Length fields accept the same entries as the Feet and Inches Calculator: 9' 6, 7 3/4", 2743mm or 3m + 6'. A plain number means inches, or millimeters when the Units panel is set to metric.