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

Connecticut's municipalities — Bridgeport, New Haven, Hartford, Stamford — review structural drawings for accessory dwellings under the Connecticut State Building Code, and the PE seal is the standard requirement. The seal must show the engineer's name, Connecticut 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 below the frost line — glacial soils are the norm — sizes beams, headers, and the lateral system, and checks snow, wind, and coastal flood design per the Connecticut State Building Code. Shoreline properties get extra scrutiny for flood elevation and wind. Garage conversions are checked for floodplain compliance where triggered. Bring the site survey, the geotechnical report, and the architectural plans. Snow-load errors are the item most ADU plans miss.

Use this checklist before engaging an engineer for your ADU: • Engineer of record holds an active Connecticut 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 • Snow loads matched to the site jurisdiction • Frost-depth compliance verified for footings, plumbing, and equipment • Garage conversions: existing slab evaluated for dwelling loads • Engineer confirms they'll respond to plan-check corrections on sealed sheets • Seal shows name, Connecticut PE number, and date on every sealed sheet