Saint Helena permitted 65 ADUs from 2013 to 2022 — among the most active markets in California. Here's what it costs, what's allowed, and who builds them.
All-in design-build estimates (architecture + permits + construction + soft costs). Real quotes vary by lot conditions, finishes and contractor — get at least three before signing.
Per-square-foot ranges reflect 2026 pricing in the default market. Permit fees ($5–25k), site work ($10–40k) and high-end finishes can push totals 20–40% higher.
California state law sets a floor that every city must meet. Saint Helena may allow more than the minimums shown — confirm with the Saint Helena planning department before finalising plans.
| Rule | Standard |
|---|---|
| ADUs allowed on single-family lot | Yes — required by state law |
| Max units per lot | 1 ADU + 1 JADU on single-family; up to 2 detached ADUs + JADU on multifamily |
| Owner-occupancy required | Not allowed to require for ADUs (state preempts) |
| Min side & rear setback (detached) | 4 feet |
| Max height (detached, single-family lot) | 16 ft — 18 ft if within 0.5 mi of major transit |
| Off-street parking | None required if within 0.5 mi of public transit (state law applies in most metros) |
| Max ADU size (detached) | 850 sqft for studio/1BR; 1,000 sqft for 2+BR (city may allow more) |
| Min lot size | No minimum required by state |
| Permit timeline (ministerial) | 60 days from complete application (state law) |
Saint Helena adopted its current ADU ordinance in 2017. Read the full ordinance text (PDF).
Annual ADU permits issued, 2013–2022. Source: Big West Coast ADU Dataset (BuildinganADU.com).
Active CA-licensed B-class general contractors with ADU-specialist branding, sourced from the CSLB Public Data Portal. Always verify license status and read recent reviews before signing.
We don't yet list ADU specialists with offices in Saint Helena. Builders from neighbouring cities often serve this area — check our full builder directory or contact your local planning department for referrals.
Most Saint Helena ADU projects fall in a $150,000–$400,000+ range, all-in (design + permits + construction). The big drivers are size, type (detached costs more than a garage conversion), and finish level. See the per-type cost table above for typical ranges in this market.
Yes — every ADU in California requires a building permit. Saint Helena processes ADU applications under the state's 60-day ministerial review rule (no public hearings, no discretionary review for code-compliant designs). Permit fees vary but typically run $5,000–$25,000 depending on size and impact fees.
State law guarantees a minimum allowance of 850 sqft (studio/1BR) or 1,000 sqft (2+BR). Many California cities allow larger detached ADUs — check the Saint Helena planning department or the ordinance link in our rules table above for the local maximum.
No. State law prohibits California cities from requiring owner-occupancy on ADUs permitted between 2020 and 2025. From 2025 onward, cities may reinstate owner-occupancy requirements — verify with your planning department before committing.
A JADU (Junior ADU) is a unit ≤500 sqft created within an existing single-family home, sharing a wall with the main residence. JADUs are cheaper and faster to build, but they require owner-occupancy of either the main house or the JADU. Most homeowners build a separate ADU for rental flexibility.
According to the California ADU permit dataset compiled by BuildinganADU.com, Saint Helena permitted 18 ADUs in 2021, the peak year on record (2013–2022). California-wide ADU permits have grown roughly 20× over that period — homeowner demand is outpacing every other housing-supply tool the state has tried.
UC Berkeley's Center for Community Innovation graded Saint Helena's ordinance A- in their 2020 ADU Scorecard (2017 ordinance text). The mean grade across California was C+, so anything above that is meaningfully homeowner-friendly. Note: state-law updates since 2020 (AB-2221, AB-976, AB-1033) have raised the floor for every city.