Is an Engineer Stamp Required for My ADU Project in Arizona?

Arizona cities — Phoenix, Tucson, Mesa, Scottsdale, Chandler — review structural drawings for accessory dwellings, and the seal of an Arizona registrant is the standard requirement. The seal must show the registrant's name, Arizona registration number, and date, and the registrant must be in responsible charge of the engineering. Detached ADUs, garage conversions, and casitas are treated the same at the structural level. Owner-builders don't escape the requirement: the building department asks for the seal regardless of who drafted the plans.

The engineer reviews the floor plan and elevations, designs the foundation for the site's expansive or collapsible soils — post-tensioned slabs are common in the Valley — sizes beams, headers, and the lateral system, and checks wind and uplift design. Garage conversions get extra scrutiny because the existing slab was rarely designed as a dwelling foundation. Monsoon drainage and site grading are coordinated with the structural design. Bring the site survey, the geotechnical report, and the architectural plans. Soil data is the item most ADU projects lack.

Use this checklist before engaging an engineer for your ADU: • Engineer of record holds an active Arizona registration, verifiable on the state roster • Dimensioned floor plan and elevations ready for structural review • Site survey showing setbacks, easements, and existing structures • Geotechnical report addressing expansive or collapsible soils for the lot • Foundation designed for soil movement, not just bearing capacity • Garage conversions: existing slab evaluated for dwelling loads • Engineer confirms they'll respond to plan-check corrections on sealed sheets • Seal shows name, Arizona registration number, and date on every sealed sheet