The short answer for most California homes
California's state ADU laws have dramatically expanded who can build. As of 2026, the vast majority of single-family lots in California qualify for at least one ADU and one JADU — many qualify for multiple ADUs. Cities cannot impose minimum lot sizes for state-mandated ADUs, and most local restrictions that used to block ADUs (like owner-occupancy, parking near transit, or excessive setbacks) have been preempted by state law.
What you actually need to check
Zoning: your property must allow residential use (almost all R-1, R-2, and R-3 zones qualify). Setbacks: state law requires only 4-foot side and rear setbacks for ADUs up to 16 feet tall. Utilities: your electrical panel, water service, and sewer line must support the additional unit, or you'll need an upgrade. Lot access: detached ADUs need a path for materials and ongoing tenant access. HOA restrictions: HOAs can impose architectural review but cannot outright prohibit ADUs.
Common deal-breakers (and workarounds)
Hillside lots with steep slopes may require expensive grading and geotechnical work. Tiny urban lots may still qualify but limit you to a JADU or small attached ADU. Properties in historic preservation overlays face additional design review. In each case there's usually a path forward — it just requires the right design strategy.
Get a definitive answer
The only way to know for sure is a site assessment. AER Builders offers free in-person ADU feasibility reviews for California homeowners — we measure the lot, check setbacks and utilities, and tell you exactly what you can build.