ADU rules in Santa Clara County

Allowed by right. Section 4.10.015 lets a 'standard ADU' be attached or detached, and the zoning use tables list Standard ADUs as R (permitted by right, with no discretionary Planning permit) in the rural A, AR, HS and RR districts, all seven urban residential districts (R1, R1E, RHS, R1S, R3S, R2, R3), the CN, CG and OA commercial districts and the A1 and RS special-purpose districts; they are barred in the ML and MH industrial districts and not listed for OS/F or SCA. A detached unit must stand at least six feet from the home, and the lot needs an existing or proposed primary residence with building site approval (4.10.015(B)(4), (D)). The codified text still limits a lot to one ADU and one JADU (4.10.015(B)(1)), but its own intent clause voids provisions that conflict with state law, and Gov. Code 66323(a) requires ministerial approval of a converted ADU, a detached new-construction ADU with 4-foot side and rear setbacks and a JADU in any combination, which the county's July 22, 2026 staff reports say it already applies. This entry covers unincorporated Santa Clara County only; San Jose, Sunnyvale and Santa Clara have their own entries.

An attached ADU shares a roof, a foundation and a common wall of at least eight horizontal feet with the home, or sits entirely within the home's living area (4.10.015(C)); an ADU may also be carved out of existing space in the home, including an attached garage, or converted from a detached accessory building, with up to 150 sq ft of expansion (4.10.015(H)). A JADU of up to 500 sq ft is allowed by right wherever standard ADUs are (Tables 2.20-1 to 2.50-1). The county text also lets a JADU sit inside a standard ADU, up to 1,700 sq ft for the pair (4.10.015(D)(6), (F)(1)), a layout state law does not treat as a JADU (Gov. Code 66333(d)) and the July 2026 draft amendment would delete. On multifamily lots, ADUs may be created in non-livable space of an existing multifamily building, at least one and up to 25 percent of the existing units (4.10.015(C)(4); Gov. Code 66323(a)(3)).

A detached ADU may have up to 1,200 sq ft of floor area, plus up to 400 sq ft of attached garage or carport and 400 sq ft of decks and porches beyond that (4.10.015(D)(1), (D)(4)-(5)). Attached ADUs scale with the home: 800 sq ft for a home of 1,600 sq ft or less, 50 percent of the home for 1,601 to 2,400 sq ft, and 1,200 sq ft for larger homes (4.10.015(C)(1)); a JADU is limited to 500 sq ft (2.10.030). The county measures gross floor area to the exterior faces of the walls, counting qualifying basement space (1.30.030), while the state floors have been measured in interior livable space since Jan 1, 2026: no size rule may block an 800 sq ft ADU with 4-foot side and rear setbacks (Gov. Code 66321(b)(3)), and a conversion under 66323(a)(1) is not subject to the county caps (HCD finding 7). Height is 16 feet when the ADU does not meet the zone's single-family setbacks (30 feet front, side and rear in the rural districts) and otherwise the zone's limit, 35 feet in the rural and most urban districts; in setback areas state law allows 18 feet within half a mile of a major transit stop or high-quality transit corridor, plus 2 feet for a matching roof pitch, and 25 feet for an attached ADU (Gov. Code 66321(b)(4)), which govern over the county's 16 feet (HCD finding 6).

No owner occupancy is required for an ADU: neither 4.10.015 nor the use tables impose one, and Gov. Code 66315 bars it. For JADUs the codified text (4.10.015(F)(4); Table 2.20-1 Note 9) still requires the owner to live in the home or the JADU in every case, unless the owner is a government agency, land trust or housing organization, and the county's JADU deed restriction form (January 2021) records that residence as a condition. Since Jan 1, 2026, Gov. Code 66333(b) (AB 1154) requires owner occupancy only when the JADU shares sanitation facilities with the home; 4.10.015(A) voids conflicting county text, and the county's July 22, 2026 staff reports and draft amendment adopt the state rule. The county's ADU page FAQ still describes the older universal JADU requirement.

One off-street space is required for a standard ADU and none for a JADU or a movable tiny home (4.10.015(I)(1); Table 4.30-1). No space is required for an ADU within half a mile of public transit service, in a -h historic preservation district, that is part of the existing home or an existing accessory structure, where on-street permits are required but not offered to the occupant, or within one block of a car share vehicle, and a converted garage or carport that held the home's covered parking need not be replaced (4.10.015(I)). State law adds an exemption the county text lacks, for an ADU applied for together with a new single-family or multifamily home (Gov. Code 66322(a)(6); HCD finding 9), and caps any requirement at one space per unit or per bedroom, whichever is less (66314(d)(10)). The parking table's note 3 defers to state law where it prohibits parking requirements, and a variance may reduce required ADU parking (5.70.040).

Ministerial. Standard ADUs and JADUs are R, permitted by right with no discretionary Planning permit, in every district that allows them, and building permit applications are reviewed ministerially and approved or denied within 60 days of a complete application (4.10.015(B)(2)); movable tiny homes need an administrative planning clearance (C). ADUs are exempt from design review (5.50.050(C)), and in the -d, -d1, -d2 and -sr design review and scenic road districts a new ADU needs only a light reflectivity value of 45 or less on facade and roof (4.10.015(J)(1)). State law adds a 15-business-day completeness check, a written list of deficiencies on denial and an appeal (Gov. Code 66317), which the county text does not yet restate (HCD finding 4). Extra steps apply in three cases: Priority List 1 and 2 historic properties in the New Almaden -h1 district get design review with a Historical Heritage Commission recommendation (4.10.015(J)(2)), Williamson Act land needs a compatible use determination before any development (Ordinance Code C13-16), and the primary residence must have building site approval (4.10.015(B)(4)).

An ADU may be rented long term, but 4.10.015(B)(5) provides that 'Accessory dwelling units shall not be rented for terms shorter than 30 days', and state law requires terms longer than 30 days for state-exempt 66323 units and JADUs (Gov. Code 66323(e), 66333(g)); the county has no short-term rental permit, and its transient occupancy tax treats stays of 30 consecutive days or less as transient lodging (Ordinance Code A30-49; 8 percent per the Department of Tax and Collections). ADUs and JADUs may not be sold separately from the home except under the qualified-nonprofit path (4.10.015(B)(3), still citing repealed 65852.26; Gov. Code 66341), and the county has not adopted a Gov. Code 66342 ADU condominium ordinance. Ord. NS-1100.137 (adopted June 23, 2026, effective Jan 1, 2027, in Municode's ordinance bank but not yet codified) replaces Division C5 with just-cause eviction and relocation rules for unincorporated rentals; an owner-occupied single-family home renting no more than two units or bedrooms, ADUs and JADUs included, is exempt except for relocation assistance after a government order to vacate for substandard conditions (C5-3(e), C5-12).