California has passed a steady stream of ADU legislation since 2016, and the rules have gotten significantly more homeowner-friendly with each round. Here's a plain-language summary of where things generally stand — though because this is state minimum law layered under local ordinances that vary city to city, treat this as a starting point for your conversation with your contractor and building department, not a substitute for checking your specific jurisdiction.
Approval is ministerial, not discretionary
For most ADUs that meet state standards, local agencies must approve the permit "by right" — no planning commission hearing, no discretionary design review, no neighbor notification requirement. This was one of the biggest changes from the 2020 reforms (AB 68 and related bills) and remains a core protection under current law.
The 60-day review clock
Once you submit a complete ADU application, the reviewing agency generally must approve or deny it within 60 days. If they don't act in that window, some jurisdictions treat the application as deemed approved. This rule has been reinforced and clarified in multiple legislative rounds because enforcement varied city to city in practice.
Size limits
- Junior ADU (JADU): generally capped around 500 square feet of interior living space, and must be created within the existing walls of the primary home.
- State-mandated detached ADU: a baseline ministerial allowance up to roughly 800 square feet applies statewide, regardless of what a local ordinance otherwise permits.
- Local "ordinance" ADUs: cities can permit larger ADUs under their own adopted ordinance, often up to 1,200 square feet or more, subject to objective (not subjective) development standards.
Height & setbacks
Detached ADUs are generally allowed up to 16 feet in height by right, with additional height (commonly up to 18 or more feet) permitted near transit or on lots with an existing multi-story structure. Standard setbacks are typically around 4 feet from side and rear property lines for qualifying ADUs — significantly less restrictive than standard single-family setback rules.
Parking
Many ADUs no longer require replacement parking — particularly units within half a mile of public transit, JADUs, and conversions of existing structures. Where parking is required, it's typically one space per unit or bedroom, and can often be provided in tandem or uncovered configurations.
Multiple units on one lot
Recent state guidance has moved toward allowing multiple ADU-type units on a single qualifying single-family lot — potentially a conversion ADU, a JADU, and a new-construction detached ADU together, each governed by its own size and approval rules. Whether this applies to your property depends on your lot's zoning and existing structures.
What this means for you
In practice, the state has removed most of the old discretionary roadblocks — but local plan-check requirements, utility connection rules, fire access standards, and coastal zone review (where applicable) still add real complexity. This is exactly the part of the process our team manages for you: we track current requirements in every city we serve and handle plan submission, revisions, and inspections so you don't have to interpret code language yourself.