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

Alabama's municipalities — Birmingham, Montgomery, Mobile, Huntsville — review structural drawings for accessory dwellings, and the PE seal is the standard requirement. The seal must show the engineer's name, Alabama PE number, and date, and the engineer must be in responsible charge of the engineering. Detached ADUs, garage conversions, and in-law additions 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 clay and expansive soils — Black Belt prairie clays get extra attention — sizes beams, headers, and the lateral system, and checks hurricane wind and seismic design. Mobile's Gulf Coast wind speeds get extra scrutiny. Garage conversions get extra attention because the existing slab was rarely designed as a dwelling foundation. Bring the site survey, the geotechnical report, and the architectural plans. Wind design is the item most ADU plans miss.

Use this checklist before engaging an engineer for your ADU: • Engineer of record holds an active Alabama PE license, verifiable on the state roster • Dimensioned floor plan and elevations ready for structural review • Site survey showing setbacks, easements, and existing structures • Hurricane wind design verified per the wind maps • Foundation designed for expansive clay soils where triggered • Garage conversions: existing slab evaluated for dwelling loads • Engineer confirms they'll respond to plan-check corrections on sealed sheets • Seal shows name, Alabama PE number, and date on every sealed sheet