IRC Section R404 requires engineered design for any retaining wall with more than 4 feet of unbalanced backfill (bottom of footing to top of retained soil). On the Wasatch Front — where most communities are in Seismic Design Category D per ASCE 7-22 — walls over 4 feet also need seismic design for lateral forces in addition to static soil pressure. In practice, most significant landscape retaining walls in Sandy, Draper, Cottonwood Heights, and other foothill communities require engineering. Walls under 4 feet can be built to IRC prescriptive standards — but even for smaller walls, frost-depth footings (30–36″) are required, and drainage aggregate and drain tile behind the wall must be provided to prevent hydrostatic pressure buildup from Utah’s snowmelt and spring rains. RainFire Builders coordinates structural engineering on all qualifying walls and manages the permit process through final inspection.