Santa Clara County ADU Rules: Why It Depends on Your City

Unlike Monterey or Santa Cruz County, Santa Clara County doesn’t apply one countywide ADU ordinance to most of the homeowners we work with here. Nearly every Santa Clara County property we build in sits inside a city, San Jose, Morgan Hill, or Gilroy, and each city sets its own specific standards on top of the state ADU law baseline. This guide explains why that matters and where to find the real numbers for your address.

The short version: Santa Clara County itself doesn’t publish a separate countywide ADU rulebook for the cities where we build. State ADU law is the floor everywhere, but San Jose, Morgan Hill, and Gilroy each layer their own specifics on top. We confirm your city’s exact rules, free, as part of the feasibility study.

Why there’s no single Santa Clara County answer

Most of our Santa Clara County work happens inside incorporated cities rather than unincorporated county land, and each of those cities administers its own ADU permitting. That means the honest answer to “what does Santa Clara County allow?” is “it depends which city your parcel is in,” not a single countywide figure. We’d rather tell you that plainly than force a one-size-fits-all number that doesn’t reflect your actual address.

San Jose: state law directly, one of the most ADU-friendly permit shops in California

San Jose applies state ADU law directly in its own zoning code, so the statewide standards effectively are the local standards here. On top of that baseline, the city runs a dedicated ADU Ally desk (adu.ally@sanjoseca.gov), offers preapproved plan sets that can shorten plan review, and allows ADU condominium conversions, meaning an existing ADU can be sold separately once a condo map is approved. A legally built San Jose home can be eligible for up to three ADUs on one property.

On fees: school and parkland impact fees don’t apply to ADUs under 750 sq ft. At 750 sq ft or larger, those fees apply and building permit fees scale with ADU size. First-round building plan review typically runs about 20 business days, inside the state’s 60-day ministerial clock.

See our full San Jose ADU guide for more detail.

Morgan Hill: state standards through Municipal Code 18.84, plus a pre-approved plans gallery

Morgan Hill follows state ADU standards through Municipal Code chapter 18.84 and runs a pre-approved plans gallery connecting homeowners directly with designers. A JADU here is up to 500 sq ft, may use an efficiency kitchen, and can share a bathroom with the main house, with the owner required to live on the property. A single-family property can have a JADU, an internal conversion or attached ADU, and a detached ADU all at once. Special zones, historic, hillside, high fire severity, or flood, can limit what’s buildable, so we confirm those details for your specific parcel.

See our full Morgan Hill ADU guide for more detail.

Gilroy: stricter size cap, but one of the fastest permit timelines in the region

Gilroy is the one city in this group where local rules are actually stricter than the state default: detached ADUs are capped at 1,000 sq ft under City Code 30.54, versus the 1,200 sq ft ceiling that applies elsewhere. In exchange, Gilroy pre-approves standardized construction plans and can issue those permits in about 15 working days when your documents are complete, among the fastest timelines in the region. Setbacks are 4 ft from side and rear lot lines, height is capped at 16 ft (up to 18 to 20 ft within a half mile of major transit), and one parking space is required unless your lot qualifies for a transit, historic-district, or car-share exemption.

See our full Gilroy ADU guide for more detail.

What’s the same across all three cities

Regardless of which Santa Clara County city your property sits in, the state-law floor applies everywhere: ministerial approval with no public hearing, a 60-day decision clock once your application is complete, and the impact fee waiver for units under 750 sq ft. What differs is the specific size caps, timelines, and local programs layered on top, which is exactly why the city-level detail above matters more than a countywide summary would.

How Framework First’s pricing handles this

Every Framework First ADU is priced all-inclusive: a permitting budget, plans, foundation, the factory build, delivery, hookups, appliances, and final inspection, running $180,000 to $557,000 across 14 models from 405 to 1,200 sq ft, delivered in 4 to 9 months. Actual permit costs differ by city, so we confirm your specific figure with San Jose, Morgan Hill, or Gilroy as part of the feasibility study. We’re family-owned, based in Salinas since January 2021 (CSLB #1047146, MFG #1595931), and we’ve built across all three cities.

Compare models and transparent pricing, or jump straight to your city: San Jose, Morgan Hill, or Gilroy.

Frequently asked questions

Why doesn’t this guide give one set of Santa Clara County numbers?

Because there isn’t one accurate answer. Most Santa Clara County properties we build for sit inside San Jose, Morgan Hill, or Gilroy, and each city sets its own specifics on top of the state baseline. A single countywide figure would be wrong for at least two of the three cities.

Which Santa Clara County city has the most ADU-friendly rules?

San Jose applies state law directly with minimal added restriction and runs a dedicated ADU support desk. Gilroy caps detached size below the state default but offers one of the fastest permit timelines in the region. Morgan Hill sits closer to the state baseline with its own pre-approved plans program. Which is “friendliest” depends on what matters most to your project.

What if my property is in unincorporated Santa Clara County?

If your parcel sits outside all three cities’ boundaries, county rather than city rules apply. We confirm this directly using parcel records as the first step of your feasibility study, since it’s not always obvious from a mailing address alone.

Does the under-750 sq ft fee waiver apply in all three cities?

Yes. It’s a state-law protection that applies statewide, including in San Jose, Morgan Hill, and Gilroy, regardless of each city’s other local specifics.

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Not sure which Santa Clara County city’s rules apply to your address? Start a feasibility study and we’ll confirm exactly what governs your specific parcel, free.