ADU Laws · 2026
Unincorporated Santa Clara County ADU Rules (2026)
If your property sits outside all 15 cities in Santa Clara County, you’re in unincorporated Santa Clara County, and your ADU permit comes from the County of Santa Clara Department of Planning and Development, not a city. The county allows ADUs in every zoning district that allows homes, offers two free pre-approved plans (800 and 1,200 sq ft), and is rewriting its ADU ordinance right now to match state law.
The short version: Outside city limits, the county permits your ADU. Standard ADUs and junior ADUs (JADUs) are allowed by right in rural and urban residential districts, with 4 ft side and rear setbacks and a 60-day decision on a complete application. The free county plans can shorten review, but they’re not offered in wildfire, flood or geologic hazard zones. On rural lots, septic and well clearance from Environmental Health comes before the building permit, so it belongs at the start of your plan. Where county text conflicts with state law, state law applies.
On this page
Who this applies to
According to the county’s Local Agency Formation Commission (LAFCO), about 95% of Santa Clara County residents live in one of its 15 cities. The rest live on unincorporated land, in two shapes:
- Urban unincorporated pockets. LAFCO maps unincorporated “islands” surrounded by cities, including San Jose, Morgan Hill, Gilroy, Cupertino and Los Gatos.
- Rural county land. Hillside and agricultural areas outside the cities, plus communities like San Martin, which has its own county planning advisory committee.
Your mailing address is not proof either way. LAFCO’s boundary maps show city limits, and the county’s Online Property Profile shows hazard zones. Our feasibility study confirms jurisdiction from county parcel records.
The county ADU ordinance today, and the update in progress
ADU rules for unincorporated land live in County Zoning Ordinance section 4.10.015. The version the state reviewed in 2025 is Ordinance NS-1200.383, adopted January 24, 2023, and the current text says:
| Standard | Current county text (section 4.10.015) |
|---|---|
| Units per single-family lot | One ADU and one JADU |
| Detached ADU size | Up to 1,200 sq ft |
| Attached ADU size | 800 sq ft if the home is 1,600 sq ft or less, 50% of the home from 1,601 to 2,400 sq ft, 1,200 sq ft above that |
| Side and rear setbacks | 4 ft, with the front setback matching the main house |
| Height | 16 ft if the ADU doesn’t meet the house’s setbacks, otherwise the house’s limit |
| JADU built into a detached ADU | Up to 500 sq ft more, 1,700 sq ft combined |
| Parking | 1 space for an ADU, waived near transit, in existing space or near car share; none for a JADU |
| Rentals | 30 days or longer |
| Decision | Within 60 days of a complete application |
On June 24, 2025, the California Department of Housing and Community Development (HCD) sent the county a findings letter saying parts of that ordinance don’t comply with state ADU law. Among the findings: height limits must allow the state minimums of 16, 18, 20 or 25 ft depending on the situation, the county must allow every unit combination state law allows, the 1,700 sq ft cap can’t block a conversion of existing space, and “other similar styled roof design” is not an objective standard.
The county’s posted amendment schedule lists the Airport Land Use Commission on October 21, 2026, the San Martin Planning Area Commission on November 18, 2026, the Planning Commission on December 17, 2026, and the Board of Supervisors in the first quarter of 2027. Until then, the county’s own ordinance says any provision that conflicts with state law is void, so state ADU law is the floor for your project today.
Rural and urban unincorporated lots
County zoning splits residential land into two families of base districts, and ADUs are allowed in both:
| District family | Zones | Standard ADU | JADU | Movable tiny home |
|---|---|---|---|---|
| Rural | A, AR, HS, RR | By right | By right | Planning Clearance |
| Urban residential | R1, R1E, RHS, R1S, R3S, R2, R3 | By right | By right | Planning Clearance |
The county notes that some provisions vary with lot size, and an ADU’s front setback follows the main house’s setback for your zone. In a design review or scenic road overlay (-d, -d1, -d2, -sr), a new ADU is still allowed by right but needs facade and roof finishes with a light reflectivity value of 45 or less.
A JADU is no more than 500 sq ft, sits entirely inside the single-family home, and needs its own entrance and an efficiency kitchen. It may share a bathroom with the main house and needs no parking space. Under state law a JADU sits inside the main house; the county’s older text also allows one inside a detached ADU.
The county’s free pre-approved ADU plans
As part of the state’s AB 1332 requirement, the county offers two pre-approved plan sets to unincorporated residents free of charge:
- 800 sq ft, 2 bedrooms, 1 bath, single story, in Standard (Traditional) or Contemporary style
- 1,200 sq ft, 3 bedrooms, 2 baths, single story, in the same two styles
Building code compliance is pre-reviewed, so staff check site items like zoning and energy code. You still submit a site plan for your lot, Title 24 energy calculations, a roof truss design from a truss manufacturer, and items the cover sheet lists, such as school and fire impact fee forms.
Unmodified plans pay the minimum plan review fee (2 hours). Modified plans need a licensed design professional’s stamp and lose expedited review. Expedited permitting is not available in the wildland-urban interface, special flood hazard or geologic hazard zones. The county’s program FAQ also limits the plans to residentially zoned unincorporated lots with a legally established single-family home or duplex, outside the wildland-urban interface, flood and geologic hazard zones, not on a historic property and with no open code enforcement case.
| County free plans | Framework First | |
|---|---|---|
| What you get | Construction drawings | A finished home with plans, a permitting budget, foundation, delivery, hookups and appliances |
| Who builds it | A builder you hire and manage | Built about 97% in our Salinas factory |
| Closest match to the 800 sq ft plan | 2 bed, 1 bath | Seven Forty-Nine (749 sq ft, 2 bed, 1 bath), $369,000 |
| Closest match to the 1,200 sq ft plan | 3 bed, 2 bath | Twelve Hundred (1,200 sq ft, 3 bed, 2 bath), $549,000 |
| Review path | Expedited, outside hazard zones | Standard ministerial review |
The county is also reviewing vendor-submitted plans for a pre-approved vendor list, and none are posted yet. Framework First homes are not part of the county’s pre-approved program, so they go through standard ministerial review. Our guide to pre-approved ADU plans in California explains how these programs work statewide.
Septic, wells and Environmental Health
Many rural parcels aren’t on city sewer or water. ADUs stay subject to the county’s septic, sewer and water supply rules, and the main house needs building site approval before an ADU permit application goes in.
The county Department of Environmental Health (DEH) requires new development on septic to get clearance before a building permit, in five steps:
- Septic (OWTS) feasibility testing
- Plan review
- Project status and approval
- Required inspections
- Environmental Health sign-off on the building permit
DEH’s Drinking Water Program handles wells and drinking water clearance. Whether your system can carry a second unit depends on soil, system condition and bedroom count, which our septic guide covers. A septic upgrade is property-specific site work outside listed pricing, confirmed in the feasibility study.
Fire, hillside and geologic hazard areas
The county has dedicated hillside districts (HS and RHS), and hazard layers shape both review and design:
- Review path. No expedited review in hazard zones, but an ADU can still be permitted there through standard review.
- Fire-rated walls. On any lot, not only in hazard zones, the county’s plan set calls for fire-rated exterior walls when the ADU sits 5 ft or less from a property line (3 ft if sprinklered), which matters at the county’s 4 ft setbacks. The set is drawn to the 2025 California codes, including the Wildland-Urban Interface Code.
- Sprinklers. Under state law (Government Code 66314), an ADU doesn’t need fire sprinklers unless the main house does.
- Access. Steep or narrow sites need foundation engineering and a crane plan, which we check early.
How Framework First works on unincorporated parcels
Every project starts with jurisdiction. The feasibility study confirms city or county, your zoning district, hazard layers, and septic and well status. It’s $497 for a standard lot or $997 for an empty lot, refunded in full minus payment processing fees if your property can’t host an ADU, and credited toward your build if you sign with us within 90 days.
Our 14 models run 405 to 1,200 sq ft and $199,000 to $599,000 all-inclusive, with a permitting budget built in along with plans, foundation, the factory build, delivery, hookups, appliances and final inspection. County building permit fees are based on construction valuation, so we confirm your figure in the feasibility study. Our Santa Clara County ADU fees guide breaks those down. Timelines run from about 4 months (best case, on our Four Fifty) to 7 to 9 months for the Twelve Hundred models, and county review is the part no builder fully controls (see our Santa Clara County ADU permit timeline). We’re a family-owned Salinas team with 40+ years of building experience (MFG #1595931).
Compare models, see pricing, or read how San Jose, Morgan Hill and Gilroy differ inside city limits in our Santa Clara County ADU rules guide.
Frequently asked questions
How do I know if my property is in unincorporated Santa Clara County?
Check the parcel, not the mailing address. LAFCO’s maps show city limits and the unincorporated islands, and the county Planning Division at (408) 299-5700 can confirm a specific parcel. Rural areas such as San Martin are county land.
Can I build an ADU and a JADU on the same unincorporated lot?
Yes. The county’s current code allows one ADU and one JADU per single-family lot. HCD’s 2025 letter says state law (Government Code 66323) also allows combinations such as a converted ADU, a new detached ADU and a JADU on one single-family lot, and the county’s update is meant to reflect that.
Do I have to live on the property?
Not for a standard ADU. State law (Government Code 66315) bars owner-occupancy requirements for ADUs, though rentals must be 30 days or longer. For a JADU, state law since January 1, 2026 requires owner-occupancy only when it shares a bathroom with the house. County pages still describe the older rule, so we confirm county practice before you design.
Can I use the county’s free plans with a factory-built ADU?
Not as a shortcut. The free plans are drawings for a home built on site, and modified plans lose expedited review. A factory-built home comes with its own plan set and goes through standard ministerial review, with the same 60-day decision on a complete application.
What if I already have an unpermitted ADU?
The county runs an AB 2533 legalization program for unpermitted ADUs and JADUs built before January 1, 2020. Eligible owners can get relief from certain zoning standards and a delay in building code enforcement of up to five years or until January 1, 2035, whichever comes first, though not for dangerous health and safety violations.
Not sure whether the city or the county reviews your ADU? Book a free Online Property Analysis and our team will check your parcel, or start a feasibility study for the full zoning, hazard and septic picture before you choose a model.
