Accessory Structures in Mountain View, CA

Mountain View maintains 160 local ordinances across all categories, and 6 of those deal specifically with accessory structures. Here is a breakdown of what the city actually requires, what is prohibited, and where Mountain View falls on the strict-to-permissive spectrum compared to other cities.

Shed & Carport Rules

A backyard shed under 120 square feet in Mountain View needs no zoning permit if it stays one story and skips a building or grading permit under Chapter 8, per City Code Sec. 36.06.50(b). Bigger sheds fall under Sec. 36.12.50: a 500 square-foot size cap, 16-foot height with a 9-foot wall plate, and a 7-foot side setback that drops to zero if the shed sits entirely in the rear yard.

Key details: Zoning-permit-exempt shed size: Under 120 sq ft, one story. Max accessory structure size: 500 sq ft. Max height / wall plate: 16 ft / 9 ft. Side setback: 7 ft (0 ft if in rear yard). Rear setback: 7 ft minimum.

Building or installing a shed that exceeds the size, height or setback standards of Sec. 36.12.50, or skipping a required building permit, is enforced as a code violation under the citywide penalty schedule in Sec. 1.7. A first infraction draws up to a $100 fine, a second within a year up to $200, and a third up to $500; a fourth violation of the same rule within one year can be charged as a misdemeanor. Sec. 1.7(c) separately makes failure to secure a required permit a misdemeanor in its own right, and each day a violation continues counts as a separate offense.

Garage Conversions

Converting a garage into living space in Mountain View is regulated as an accessory dwelling unit conversion under City Code Sec. 36.12.95. The city waives replacement parking entirely when a garage is converted, and lets the converted structure keep its existing height, setbacks and footprint instead of meeting current standards, so long as the new use fits the old walls.

Key details: No replacement parking: Waived for converted garages, Sec. 36.12.95(a)(6). Height/setback exemption: If same footprint as old structure, Sec. 36.12.95(b)(3). Entry expansion allowed: Up to 150 sq ft for ingress/egress, Sec. 36.12.95(b)(2). Utility connection fees: Waived for existing-space conversions, Sec. 36.12.115(b). Nonconforming corrections: Required only if a health/safety threat, Sec. 36.12.110.

Converting a garage without a permit is treated the same as any unpermitted structure: a code violation under Section 36.12.110, which can trigger a correction order once the chief building official determines the work threatens health or safety, plus standard building-permit enforcement. General code violations are punishable as infractions ($100 first offense, $200 second, $500 for each additional violation within a year) or as a misdemeanor for a fourth violation within twelve months, under Section 1.7 of the City Code.

ADU Rules

A single-family lot in Mountain View can add one accessory dwelling unit plus one junior ADU under Sec. 36.12.75(a). Sec. 36.12.80 caps a single-family ADU at 850 square feet (one bedroom or fewer) or 1,000 square feet (two-plus bedrooms), with a 4-foot side and rear setback and a 28-foot height limit.

Key details: Units allowed: 1 ADU + 1 JADU per single-family lot. Max size: 850 sq ft (1BR) / 1,000 sq ft (2+BR). Max height: 28 ft, 1-2 stories. Side/rear setback: 4 ft minimum. Parking: 1 space, waivable under Sec. 36.12.95.

Building an ADU that exceeds the size, height or setback standards of Sec. 36.12.80, or renting a small ADU short-term in violation of Sec. 36.12.105, is enforced under the city's general penalty schedule at Sec. 1.7: up to $100 for a first infraction, $200 for a second within a year, and $500 for each further violation, with a fourth violation in one year chargeable as a misdemeanor. Failing to obtain a required building permit is independently a misdemeanor under Sec. 1.7(c).

ADU Owner Occupancy

Building a junior accessory dwelling unit in Mountain View requires at least one legal owner to occupy one of the dwellings on the property, per Sec. 36.12.90. A deed restriction recording that requirement at the Santa Clara County Recorder's office must be on file before the city issues a building permit for the JADU.

Key details: Applies to: Junior ADUs (JADUs) only. Requirement: 1 legal owner must occupy 1 dwelling on lot. Exception: Government agency, land trust, housing org. Deed restriction recorded at: Santa Clara County Recorder. Deed restriction also bars: Rentals under 30 days; separate sale.

The city will not issue a building permit for a junior accessory dwelling unit until the Sec. 36.12.90 deed restriction is recorded and filed. Once built, violating the owner-occupancy condition, renting the JADU short-term in breach of the deed restriction, or selling it apart from the main house is enforceable under the city's general penalty schedule at Sec. 1.7, escalating from up to $100 for a first infraction to $500 for repeat violations within a year, with a fourth violation in one year chargeable as a misdemeanor.

ADU Impact Fees

Mountain View exempts accessory dwelling units from its citywide transportation impact fee under City Code Sec. 43.8.a.3. The fee otherwise applies per new dwelling unit for residential development citywide, but ADUs defined in Chapter 36 are carved out entirely, alongside affordable housing units and temporary uses.

Key details: Fee basis: Per new dwelling unit, Sec. 43.5.b.1. ADU exemption: Full exemption, Sec. 43.8.a.3. Also exempt: Affordable housing, temporary uses. Fee timing: Paid before building permit issued. Appeals: Zoning administrator, then council hearing.

There is no separate ADU-specific penalty; the general fee-payment rule controls. If a project is later found not to qualify as an ADU, or misrepresents its status, the transportation impact fee must be paid in full before a building permit is issued or a subdivision map recorded (Sec. 43.5.c). Classification disputes go to the zoning administrator, and appeals of a zoning administrator's impact-fee determination are filed under Sec. 43.9 for a public hearing before the city council per Section 36.56.

The rules around adu impact fees in Mountain View lean permissive, but that does not mean anything goes.

ADU Rental Restrictions

Mountain View lets owners rent an accessory dwelling unit or junior ADU independently of the main house under City Code Sec. 36.12.100, but forbids selling either unit separately from the primary dwelling. Section 36.12.105 then bars short-term rentals of 30 days or less in most of those same units, including every JADU and every ADU of 800 square feet or smaller.

Key details: Independent long-term rental: Allowed for ADUs/JADUs, Sec. 36.12.100. Separate sale: Prohibited, must stay with primary dwelling. Short-term rental ban: 30 days or less, Sec. 36.12.105. Units covered by STR ban: All JADUs and ADUs 800 sq ft or smaller. Exception path used: Detached units under 36.12.95(b)(1) still banned.

Renting a covered unit for stays of 30 days or less, or attempting to sell an ADU or JADU apart from the primary dwelling, is a violation of this code enforceable under Section 1.7: prosecutable as an infraction with fines of $100 for a first offense, $200 for a second within a year, and $500 for each additional violation, or as a misdemeanor if a fourth violation occurs within twelve months. Each day the violation continues is a separate offense.

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

The Bottom Line

Mountain View's accessory structures rules are a mixed bag. Some areas are strict, others are relaxed, and the details matter. The best approach is to check the specific rule that applies to your situation rather than assuming Mountain View is broadly strict or permissive.

All of the above reflects Mountain View'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.