ADU rules in Sunnyvale

Detached ADUs are allowed on any lot in a residential or residential mixed-use zone with an existing or proposed single-family home or multifamily building (SMC 19.79.020); Table 19.18.030 sends ADUs in R-0/R-1, R-1.5, R-1.7/PD, R-2, R-3, R-4 and R-5 to Chapter 19.79, and the Downtown Specific Plan does the same in every block. A single-family lot may have one new-construction ADU (attached or detached), one conversion ADU and one JADU, three units besides the house (19.79.050(a)(1)). A detached unit up to 800 sq ft with 4-foot side and rear setbacks needs only a building permit; one from 800 to 1,000 sq ft needs a ministerial Miscellaneous Plan Permit and meets added objective standards such as zoning front setbacks and 5 feet from the house (19.79.030, 19.79.040(g), (w)). On multifamily lots up to eight detached ADUs are allowed beside an existing building (never more than its unit count) and two beside a proposed one, all streamlined (19.79.060(a)).

On single-family lots an attached ADU may be new construction (a physical expansion of the house beyond the 150 sq ft ingress and egress allowance) or a conversion of space inside an existing or proposed house or accessory structure; a lot may have one of those two attached types, not both, plus a JADU of up to 500 sq ft inside the house, including an attached garage (19.12.020(1), 19.79.050(a)(3), (d)). Attached new construction up to 800 sq ft and every conversion or JADU need only a building permit; attached units over 800 sq ft need a ministerial MPP, must match the house's cladding, trim, roofing, colors and window frames, and may not put their entrance on the same street-facing wall plane as the house (19.79.040(f), (i)(1)). Attached new construction is not an ADU type on multifamily lots; there, at least one and up to 25 percent of the existing units may be created by converting non-habitable space such as storage rooms, attics, basements or garages (19.79.060(b)).

New-construction ADUs on single-family lots are capped at 1,000 sq ft of gross floor area with no bedroom limit and no percent-of-house limit for attached units (19.79.050(b)(1)); area is measured from the outside dimensions of the walls (19.79.040(a)), the minimum is 150 sq ft, and the first 800 sq ft of each ADU is excluded from lot coverage and FAR (19.12.080(12)(c), 19.12.130(16)). Conversion ADUs have no maximum (with up to 150 sq ft of expansion for ingress and egress), JADUs are capped at 500 sq ft inside the house, and Table 19.79.070 note 2 confines the 1,000 sq ft cap to single-family lots, so detached units on multifamily lots have no local size cap. Detached height is 16 ft on single-family or one-story multifamily lots, 18 ft within half a mile walking distance of a major transit stop or high-quality transit corridor (plus 2 ft to match the house's roof pitch) and 18 ft on multistory multifamily lots; attached units may reach 25 ft or the main building's limit, whichever is lower, and no ADU may exceed two stories (19.79.040(k), (n)). Gov. Code 66321(b)(2), as amended by SB 543 effective 1-1-2026, bars a local maximum below 850 sq ft of interior livable space, or 1,000 sq ft of interior livable space for a unit with more than one bedroom; because Sunnyvale's 1,000 sq ft cap is measured from outside walls, a two-bedroom unit may claim 1,000 sq ft of interior livable space under the state floor (66325(a)), a point Ord. 3258-26 left unaddressed.

Sunnyvale imposes no owner-occupancy requirement on ADUs, in line with Gov. Code 66315, which bars owner-occupant requirements for ADUs. The only owner-occupancy rule is for a junior ADU that shares sanitation facilities with the house: the JADU or the rest of the house must be the bona fide principal residence of a legal owner, shown at building permit approval, backed by a recorded covenant that also bars separate sale, caps the JADU at 500 sq ft and requires rentals longer than 30 days (19.79.050(d)(7)). Ord. 3258-26 (adopted 7-28-2026, effective 8-27-2026) narrowed that rule from every JADU to shared-sanitation JADUs to track AB 1154 and Gov. Code 66333(b); the city's toolkit applied the narrower rule from January 2026. A new-construction ADU is treated as a JADU only if the owner accepts the JADU owner-occupancy and deed restrictions (19.79.050(d)(6)).

No off-street parking is required for any ADU anywhere in the city, and covered spaces removed or demolished to build an ADU or convert space in the house or an accessory structure need not be replaced (19.79.040(o)); the parking chapter repeats that no replacement parking is owed when a garage or carport is converted to an ADU or demolished to build one (19.46.050(e)). This is more generous than Gov. Code 66314(d)(10), which would let a city require up to one space per unit or bedroom outside the 66322 exemptions; the state bar on replacement parking (66314(d)(11)) also covers uncovered spaces, which the local text does not mention.

Every ADU is approved ministerially. Streamlined units (new construction up to 800 sq ft on single-family lots, detached units on multifamily lots, conversions, JADUs and units entirely within a basement) need no planning permit, only a building permit (19.79.030(a)). New construction over 800 sq ft on a single-family lot needs a Miscellaneous Plan Permit that the Community Development Director decides ministerially without notice or hearing, appealable only by the applicant or owner (19.79.030(b), 19.82.030(b)); the city brochure gives a typical 2 to 4 week MPP review before the building permit. Ord. 3258-26 added the Gov. Code 66317 clock: written completeness notice within 15 business days, and a decision within 60 days of a complete application (19.79.100). Lots on the Heritage Resource Inventory face no added permit or public review (19.79.040(l)).

An ADU may be rented separately from the main home but may not be sold or conveyed separately except under Gov. Code 66341 (a unit built by a qualified nonprofit and sold to a qualified buyer under a recorded tenancy-in-common agreement), and the code states that the city has not opted into the 66342 ADU-condominium program (19.79.040(q)). Sunnyvale defines a short-term rental as transient lodging for 30 consecutive calendar days or less and prohibits it citywide except approved hosted rentals (19.76.020, 19.76.030); ADUs approved on or after 1-1-2020 may not be short-term rentals at all, while a pre-2020 ADU may be a hosted STR if the host lives on the lot, with director approval, the approval number on every listing, a business license for three or more listings and the 12.5 percent transient occupancy tax (19.79.040(r), 19.76.040 to 19.76.050; city STR page). The practical minimum rental term is therefore longer than 30 days, which also satisfies Gov. Code 66323(e) for state-exempt units; JADU covenants separately require rentals longer than 30 days (19.79.050(d)(7)(A)(iv)).