Utah has adopted IECC 2021 for residential construction. Most Wasatch Front valley communities are Climate Zone 5: R-49 attic, R-20 wall (R-13+5 CI), R-30 floor over unconditioned space, U-0.30 maximum windows, and 5.0 ACH50 air leakage maximum verified by mandatory blower door test. Mountain communities (Park City, Heber, Brian Head) are Climate Zone 6 with the same insulation requirements. IECC 2021’s mandatory blower door test is the most important addition to the 2021 edition — it verifies that air sealing actually achieves code compliance rather than relying on visual inspection alone. REScheck energy compliance documentation is required with the permit application in most Utah jurisdictions. RainFire Builders prepares REScheck documentation as a standard part of every permit package.