How Sunnyvale Handles Accessory Structures: A Practical Guide

Sunnyvale maintains 146 local ordinances across all categories, and 5 of those deal specifically with accessory structures. Here is a breakdown of what the city actually requires, what is prohibited, and where Sunnyvale falls on the strict-to-permissive spectrum compared to other cities.

Garage Conversions

Converting a garage or carport in Sunnyvale to a non-parking use needs a miscellaneous plan permit and, outside the ADU exception, requires replacing every lost space with a new covered space that meets current standards under Section 19.46.050(e).

Key details: Permit required: Miscellaneous plan permit. Replacement requirement: One covered space per space converted. ADU exception: No replacement if converted to an ADU. Minimum covered spaces (SFD/duplex): 2 of 4 total, not tandem. Governing code: SMC § 19.46.050(e).

Converting a garage without the required miscellaneous plan permit and replacement covered space is an infraction under Section 1.04.010(b)(9) (Title 19 infractions, excluding Chapters 19.67 and 19.69). Since no specific fine is listed, penalties follow Government Code Section 36900 per Section 1.04.020(b)(3); a defendant with three or more convictions in the prior year faces elevation to a misdemeanor, up to $1,000 in fines and/or six months in county jail under Section 1.04.020(c). The city may also treat an unpermitted conversion as a public nuisance under Section 19.98.200, subject to abatement and cost recovery under Section 1.04.020(d), and the director of community development enforces Title 19 permit compliance under Section 19.98.180.

This is one of the stricter rules in Sunnyvale's municipal code. If you are unsure whether your situation complies, it is worth checking with the city before proceeding.

ADU Rules

Sunnyvale allows accessory dwelling units on residential lots subject to detailed numeric standards in Section 19.79.040: a 150 square foot minimum, height caps of 16 to 18 feet detached or 25 feet attached, a two-story maximum, and zero required off-street parking.

Key details: Minimum ADU size: 150 square feet. Detached height cap: 16 ft (18 ft near transit). Attached height cap: 25 ft or main building height, lower. Story limit: 2 stories maximum. Parking: Zero off-street spaces required.

An ADU proposal that does not meet the minimum area, height, story count, setback or parking standards in Section 19.79.040 does not qualify for ministerial approval and is denied or returned for revision by the community development department; a unit built or converted to ADU use without an approved building or planning permit is subject to standard code enforcement as an unpermitted structure under Title 19.

ADU Rental Restrictions

Sunnyvale bars any accessory dwelling unit approved on or after January 1, 2020 from ever being used as a short-term rental. Section 19.79.040(r) makes the ban a permanent condition of the ADU itself, cross-referenced against the short-term rental chapter regardless of who lives on the property.

Key details: Rule: Post-2020 ADUs cannot be short-term rentals. Pre-2020 ADUs: Allowed as STR if host resides on the lot. Urban lot split units: Chapter 19.78 units never allowed as STR. Governing sections: SMC 19.79.040(r) and 19.76.040(a)(5). Ordinance: Ord. 3240-25, effective 4/8/2025.

Advertising or operating a post-2020 ADU as a short-term rental is treated as an unapproved short-term rental under Chapter 19.76: it does not qualify for hosted-rental approval under Section 19.76.050, and the city attorney may abate it as a public nuisance under Section 19.76.090.

Compared to other cities, Sunnyvale takes a harder line on adu rental restrictions. The enforcement and penalty structure reflects that.

Shed & Carport Rules

Accessory structures in Sunnyvale's single-family and duplex zoning districts cap out at 450 square feet each, with a hard citywide ceiling of 800 square feet total per lot, under Municipal Code Section 19.40.020. Structures over 450 square feet need a use permit, while smaller sheds and detached spaces follow a sliding scale of no-permit, minor-permit or use-permit review keyed to height and yard location.

Key details: Max size per structure: 450 sq ft without a use permit. Absolute lot cap: 800 sq ft total, all structures. Max height: 15 feet without a use permit. Zero setback option: Under 120 sq ft, 8 ft tall. Larger structure setback: 20 ft front, 10 ft rear.

Building an accessory structure larger than 450 square feet, taller than 15 feet, or closer than the required setback without the corresponding use permit or minor planning permit under Table 19.40.030 is a zoning violation subject to code enforcement by the community development department, which can order removal or modification and withhold approval until the structure is brought into compliance or a retroactive use permit is obtained.

ADU Owner Occupancy

Sunnyvale requires the property owner to live on site whenever a junior accessory dwelling unit is created. Section 19.79.050(d)(7) makes owner-occupancy of either the JADU or the main house a recorded deed covenant before the building permit issues; standard ADUs carry no such requirement.

Key details: Applies to: Junior accessory dwelling units (JADUs) only. Requirement: Owner-occupancy of JADU or main residence. Recorded: Deed covenant before building permit issues. JADU size cap: 500 square feet maximum. Standard ADUs: No owner-occupancy requirement, § 19.79.040(q).

The city withholds the building permit until the applicant records the owner-occupancy and no-separate-sale covenant required by Section 19.79.050(d)(7)(A). Because the covenant is recorded on title and expressly enforceable against future purchasers, selling the JADU separately from the single-family residence or discontinuing owner-occupancy in violation of the recorded covenant is a title-based breach that runs with the land.

This is not one of those rules that cities tend to ignore. Sunnyvale actively enforces its adu owner occupancy requirements.

The Bottom Line

Sunnyvale is tougher than many cities when it comes to accessory structures. Out of the 5 rules covered here, 3 are rated strict. If you are a homeowner, renter, or business owner in Sunnyvale, take the time to understand these requirements before they become a problem. Most violations come with fines, and some repeat violations can escalate.

All of the above reflects Sunnyvale's municipal code as of our last review. If you need specifics on fines, exemptions, or filing requirements, the detailed ordinance pages linked above have the full breakdown.