What are the ADU rules where you live?
Pick your county, then your city — or leave both blank for the statewide baseline that applies everywhere in California.
Statewide baseline, from CA Gov. Code §§ 66310–66342.
State law guarantees at least 850–1,000 SF, and lets cities allow up to 1,200 SF.
Setbacks can't exceed 4 ft on the sides or rear for new construction; conversions need none.
16 ft is the statewide floor, rising to 18–20 ft near transit or on multi-story lots.
At most 1 space is required, and most lots qualify for a waiver (transit, historic, car-share).
Cities must approve or deny within 60 days, with no public hearing.
No statewide fee; ADUs of 750 SF or less skip impact fees, and 500 SF or less skip school fees.
California State Law — Applies Everywhere
These rules apply no matter which city you're in. Local rules (above) can be more generous than these, but a city can never be stricter than what state law guarantees you.
California's ADU law, reorganized in 2024 and updated for 2026.
Cities can't require you to live on-site for a standard ADU. A junior ADU that shares a bathroom with the house still requires it.
Cities are allowed to require that ADU rentals last 30 days or longer, so check your city's rule before listing it short-term.
Cities can set their own standards, but can't use them to block an ADU of at least 800 SF with 4 ft side and rear setbacks.
The city has 15 business days to say your application is complete, then 60 days to approve or deny it with no public hearing.
Size limits count interior livable space, not exterior walls or the garage.
ADUs of 750 SF or less (junior ADUs 500 SF or less) can't be charged impact fees; larger ADUs pay a share based on size.
ADUs and junior ADUs of 500 SF or less are exempt from school fees; above that, districts may charge up to $5.38 per SF (2026 cap).
A city can't deny a permit for an ADU built before 2020 just because of code violations, unless it's unsafe.
State law requires cities to create a pre-approved ADU plan program; how far along yours is varies.
Starting Jan 1, 2027, cities must approve up to two new detached ADUs on a lot with a single-family home, each with side and rear setbacks of 4 ft or less.
From Jan 1, 2027, HOA rules and deed covenants can't ban or unreasonably restrict an ADU on a lot zoned to allow a single-family home, even in a multifamily zone.
Starting Jan 1, 2027, for up to two ADUs on a lot, a city can charge impact fees only on the square feet above 750, not on the whole unit.
State law current as of October 2026.
Pre-approved plans
Under California's AB 1332, every California city and county is required to offer a catalog of pre-approved ADU plans — no population threshold — designs that have already cleared building-code review, so permitting moves faster. Pick a city above to see what's available where you live.
Construction Cost Trends
Rising· partial-yearIf a bid looks higher than you expected, it's probably not your contractor padding the price — California construction costs have been climbing noticeably faster than everyday inflation.
Dashed segment = partial-year figure — not a completed calendar year yet.
Tracks how much it actually costs to build in California — labor and materials, for real construction projects here. This is the most relevant line for your ADU bid.
A nationwide version of the same idea — construction costs across the whole US, not just California. Useful for checking whether what you're seeing is a California-specific spike or a national trend.
The standard "cost of living" number you hear about on the news — groceries, gas, rent, everything, not construction specifically. It's here for comparison, to show how much faster building costs are rising than prices in general.
Each index is re-based so 2022 = 100, for direct comparison. Sources: California Construction Cost Index, Turner Building Cost Index, US Consumer Price Index (CPI-U). Data current as of September 2026, refreshed quarterly.
What Would My Old Estimate Cost Today?
See what a past bid or budget number would run in today's dollars, based on California construction cost trends.
This is planning guidance, not licensed engineering advice. Numbers and layouts here are estimates to help you plan — always confirm site-specific details with a licensed professional before you build.
A full lot-feasibility deep-dive is coming soon, pending our FutureLot data partnership — for now, this runs the cost & cost-benefit numbers from Plan It.