ADU builders
Two-story ADU: height rules and who builds it
By the HyreADU research desk. Last checked .
The short answer
A two-story ADU fits more floor area on a small footprint. In California the state height floor for a detached ADU is 16 feet, or 18 feet near transit plus two for roof pitch, which rarely fits two stories.
An attached ADU gets 25 feet (Gov. Code § 66321). So a detached two-story unit usually depends on your city allowing more.
Height is the first question
The state sets floors, not ceilings. Cities may allow taller units, and many do on larger lots. Check your local ADU rules before you design. Our California ADU ordinance tracker shows local rules we have recorded.
What a second story adds
Stairs that meet code, structural bracing for the upper floor, a stronger foundation, and often a structural engineer. Privacy rules, such as window placement facing neighbors, may apply locally.
Above-garage units
A unit over a garage is a common two-story form. The existing garage was not built to carry a dwelling, so a structural upgrade is the norm. California does not require you to replace parking lost to an ADU conversion (Gov. Code § 66314(d)(11)).
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
Can a detached ADU be two stories in California?
Only where your city allows more than the state height floor.
Does a two-story ADU need an engineer?
Usually, because a second story departs from simple framing.
Does the second floor count toward the size limit?
Yes. Floor area counts on every level.
Is a two-story ADU harder to rent?
Stairs limit some tenants, such as older adults. Consider who will live there.
Sources
- Gov. Code § 66321 (size and height floors). Checked September 5, 2026.
- Gov. Code § 66314 (ADU standards, parking, sprinklers). Checked September 5, 2026.
- Bus. & Prof. Code § 5537 (plans exempt from architect licensing). 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.