Utah’s residential energy code (IECC 2021 with local amendments) sets window performance requirements by climate zone. Wasatch Front valley communities — Sandy, Draper, Salt Lake City, Provo, Ogden, and surrounding cities below approximately 5,500 feet — fall in IECC Climate Zone 5: maximum U-factor 0.30 and maximum SHGC 0.40 for vertical fenestration in most residential applications. Mountain communities above approximately 5,500–6,000 feet — Park City, Heber City, Midway, Coalville — fall in Climate Zone 6: maximum U-factor 0.27. These requirements apply to new construction windows and to full window assembly replacements. U-factor measures heat loss rate — lower is better. SHGC measures solar heat gain — south-facing Utah windows can benefit from higher SHGC for passive solar. RainFire Builders confirms the applicable zone for each project address before specifying products.