Can I actually add an ADU here?
California, Oregon, Washington, Vermont, Montana, Massachusetts, and Colorado all have state-level ADU preemption laws. We translate the laws into a feasibility verdict for your ZIP, lot size, and proposed unit — and tell you when local zoning is the binding constraint.
- Cost range
- $200,000 – $360,000
SB 9 (2021) + AB 1033 (2023) + AB 976 (2023) + SB 477 (2024): California has the most permissive state-level ADU regime in the US. AB 1033 allows ADUs to be sold separately as condos. AB 976 made parking exemptions permanent. Most jurisdictions cannot enforce owner-occupancy on ADUs built after 2020.
Estimate only. Outputs are computed from publicly disclosed calibration constants and your inputs. Confirm any number with a licensed contractor or local building department before relying on it for a contract or filing.
Methodology
We map your ZIP to a state, then look up that state's ADU rules. Seven states have explicit state-level preemption (CA, OR, WA, VT, MT, MA, CO); six others (NY, TX, FL, AZ, NJ, GA) are tracked but governed by local zoning. The feasibility score weights state-law presence (25 points), proposed-size compliance with state minima/maxima (20), lot-size adequacy (15), and parking-exemption status (10). Plus 30 baseline points if a state rule exists.
Verdicts: 85+ = very likely, 70-84 = likely, 50-69 = uncertain, under 50 = unlikely. The verdict is a state-law-level signal, not an address-specific guarantee. Local zoning, lot setbacks, FAR, historic-overlay status, and slope/access conditions can all reduce feasibility below the state-level estimate.
Cost range is a state-of-the-art 2026 estimate at $250-450/sf for typical detached site-built ADUs. Coastal premium markets and luxury finishes push the upper end higher; pre-fab vendors offer turnkey pricing in the $200-400K range for similar sizes.
How this differs from Angi or Thumbtack
Angi and Thumbtack do not provide ADU feasibility analysis. Houzz Pro has ADU-specific photo galleries but not feasibility scoring. The structural value of this tool is treating feasibility as a state-law-aware question first, then a zoning-and-cost question second.
For address-specific feasibility, a licensed contractor or permit expediter can verify your specific lot's setbacks, FAR limits, historic-overlay status, and utility-capacity constraints. AskBaily's chat interface can route you to a contractor who has built ADUs in your specific city.
Frequently asked questions
Why does my California ZIP score so high?
Because California has the most permissive state-level ADU regime in the US. SB 9, AB 1033, AB 976, and SB 477 collectively make ADUs by-right on most R-1 lots, with broad parking-exemption and no owner-occupancy requirement. The state-level verdict will be 'very likely' for most California ZIP codes.
Why is my New York ZIP scoring lower than California?
Because New York has no state-level ADU preemption law. The 2023 Hochul ADU mandate was removed from the budget. ADUs in New York are entirely a local-zoning question; NYC's HIC + DOB process is the heaviest in the country. The 'unlikely' or 'uncertain' verdict reflects the state-law gap.
What if I'm in a state not in the registry?
The tool returns a generic 'uncertain' verdict and a cost range. ADU feasibility in non-registry states is determined entirely by local zoning. The recommended next step is to contact your city's planning department or a permit expediter for an address-specific zoning verification.
Does this account for AB 1033 separate-sale opt-in?
Not directly. AB 1033 is a separate question (can the ADU be sold separately as a condo) from feasibility (can it be built at all). California ZIP codes score the same regardless of AB 1033 opt-in status; we recommend checking the Casita Coalition's AB 1033 opt-in registry separately if separate-sale is in your plan.
What is the typical project timeline?
9-18 months end-to-end for a detached ADU. Design + engineering: 2-4 months. Permitting: 4-12 weeks in California, 8-16 weeks elsewhere. Construction: 5-10 months site-built, 3-6 months pre-fab-on-foundation. JADU conversions are substantially faster (3-6 months total).
Want Baily to do this for you?
Skip the calculator. Tell Baily your project and city — she will do the math, cite the local source, and pre-seed your scope.