ADU builders
Structural engineer for an ADU: when you need one
By the HyreADU research desk. Last checked .
The short answer
A structural engineer for an ADU is needed when the design leaves conventional wood framing. In California, Bus. & Prof. Code § 5537 says the building official must then require plans or calculations for that part from a licensed engineer or architect. Above-garage units, hillsides, long spans and second stories usually need one.
Projects that usually need stamped calcs
Above-garage ADUs: the garage was built for a car and a roof, not a dwelling. Hillside lots: foundations and retaining walls. Two-story units: lateral bracing and hold-downs. Conversions that remove walls or posts. Large openings such as wide sliding doors.
Your city may also ask for engineering in a high seismic zone or on poor soil. See soils report.
What the engineer delivers
Calculations and drawings for the foundation, framing, beams, shear walls and connections, stamped by a licensed engineer. They answer plan check comments on that part and may visit the site during framing.
How to check and hire one
Look up the license on the Board for Professional Engineers, Land Surveyors, and Geologists site. Ask for ADUs they engineered in your city, whether the fee covers plan check corrections, and whether site visits are included.
What to do next: read the questions to ask an ADU builder, check what decides ADU cost, then tell us about your project. Matching is not live yet, so we reply with information, not a quote.
Get ADU optionsQuestions
Does every ADU need an engineer?
No. A conventional single-story wood-frame unit often does not. The building official decides.
Can my designer do the structural work?
Only for conventional framing. Anything outside it needs a licensed engineer or architect.
Does a garage conversion need one?
Sometimes, if walls come out or the slab must carry new loads. Ask your city.
Does a prefab ADU need one?
The foundation design usually does. See modular ADU.
Sources
- Bus. & Prof. Code § 5537 (plans exempt from architect licensing). Checked October 27, 2026.
- California Board for Professional Engineers, Land Surveyors, and Geologists, license lookup. Checked October 27, 2026.
- 2022 California Residential Code, R401.4 (soil tests). Checked October 27, 2026.
HyreADU is a publisher. It does not design, permit or build ADUs, has no partner builders, and gives no legal, tax or engineering advice. Rules vary by state and city; California rules are labeled as such.