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

Delaware's counties and towns — Wilmington, Dover, Newark, New Castle County — review structural drawings for accessory dwellings, and the PE seal is the standard requirement. The seal must show the engineer's name, Delaware 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 sandy coastal soils and the high water table, sizes beams, headers, and the lateral system, and checks wind, snow, and flood design. Beach communities get extra scrutiny for flood elevation and opening protection. 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 Delaware 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 sandy 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, Delaware PE number, and date on every sealed sheet