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

Maryland's counties — Montgomery, Prince George's, Baltimore County, Anne Arundel — review structural drawings for accessory dwellings under the Maryland Building Performance Standards, and the PE seal is the standard requirement. The seal must show the engineer's name, Maryland 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 county asks for the seal regardless of who drafted the plans.

The engineer reviews the floor plan and elevations, designs the foundation for clay soils and the high water table, sizes beams, headers, and the lateral system, and checks snow, wind, flood, and seismic design per the Maryland Building Performance Standards. Bay-area properties get extra scrutiny for flood elevation. Garage conversions are checked for floodplain compliance where triggered. Bring the site survey, the geotechnical report, and the architectural plans. Flood design is the item most ADU plans miss.

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