The statewide height baseline
California Government Code requires cities to allow detached ADUs at least:
- 16 feet in most cases.
- 18 feet if the property is within a half mile of a major transit stop, or if the ADU is on a lot with a multifamily building.
- 18 feet for two-story ADUs in many cases.
- 25 feet when matching the main house height in some attached scenarios.
Cities can allow taller ADUs, but they cannot require shorter.
How height is measured
Height is measured from grade (the ground at the building) to the highest point of the roof. A flat roof at 16 feet uses the entire envelope; a pitched roof at 16 feet has less interior volume because the peak counts.
What the height limit means for design
- Single-story ADUs: Easily fit within a 16-foot limit with 9- to 10-foot interior ceilings.
- Two-story ADUs: Usually need the 18-foot allowance and careful roof design.
- Loft spaces: Adding a sleeping loft inside a single-story envelope is a common way to add usable area without exceeding height limits.
Local overlays that can change height
- Hillside ordinances may impose stricter height limits.
- Historic districts often cap heights to match neighborhood character.
- Airport flight path overlays restrict heights near airports.
- HOA covenants can be stricter than city code.
How to confirm your specific limit
Look up your property on your city's zoning portal. The zoning designation (e.g., R1, R2, RS-5) plus any overlay districts will tell you the exact height allowed. Your ADU builder should confirm this in writing before drafting plans.
Related reading
Frequently asked questions
Can I build a two-story ADU anywhere in California? State law guarantees the allowance in many cases but check local zoning and overlay districts.
How is height measured on a sloped lot? From the average grade around the building footprint.
Do roof solar panels count toward height? Typically no, but check your local code for specifics.