Building an ADU in Santa Rosa

What you can build in Santa Rosa

ADUs are allowed on any lot that allows single-family or multifamily homes and has a home on it or planned. The rules are in Santa Rosa City Code section 20-42.130, last amended in March 2026, and the city summarizes them on its ADU page. ADUs don't count against General Plan density limits.

Single-family lots. You can have up to two ADUs and one junior ADU: one new attached or detached ADU, one ADU converted from space in the house or an accessory building, and one junior ADU.

Multifamily lots. You can convert non-living space (storage rooms, attics, basements, garages) into ADUs, at least one and up to 25% of the existing units. You can also build up to eight detached ADUs on a lot with an existing multifamily building (no more than the existing units), or two with a proposed one. Up to two new attached ADUs are allowed too.

SB 9 lots. If you use both SB 9 tools, a two-unit project and an urban lot split, the city allows at most one ADU (and one junior ADU) per lot. Only on lots outside the Wildland Urban Interface with a street at least 36 feet wide (parking both sides) or 30 feet wide (parking one side). See our SB 9 guide.

Statewide rules are on our California page. [1][2]

Size, height and setbacks

Size

• New detached ADU: up to 1,200 sq ft of habitable space.
• New attached ADU: up to 50% of the existing home's square footage, but 850 sq ft (studio or one bedroom) or 1,000 sq ft (more than one bedroom) is always allowed.
• Conversion inside the house: up to 45% of the home's habitable space (not counting the garage) and no more than 1,200 sq ft, with the same 850/1,000 sq ft minimums.
• Conversion of a detached accessory building: up to 1,200 sq ft, within its existing dimensions plus 150 sq ft for an entrance.

Height

• One story: 16 feet, or 18 feet to match the main home's roof pitch.
• Detached ADU within a half-mile walk of a major transit stop or high-quality transit corridor: 18 feet, or 20 feet to match the roof pitch.
• Attached to the home: 25 feet.
• Two stories: 27 feet. No ADU can exceed 27 feet, and an ADU over a garage or carport can't make the combined structure taller than 27 feet.

Setbacks. New ADUs need 4-foot side and rear setbacks and 8 feet on a street side. The front setback matches the main home's, but an 800 sq ft ADU may go in the front setback if there is no other place for it. An ADU above a garage needs 5-foot side and rear setbacks. Converting existing legal space needs no setback. In multifamily zones, no side or rear setback is needed next to an R-3 zone.

Lot coverage follows the zone, but it can't block an 800 sq ft one-story ADU with 4-foot setbacks. The city's ADU page lists 40% lot coverage for new ADUs in single-family zones.

Hillsides and creeks. On slopes of 10% or more, an ADU over 800 sq ft or above one-story height needs 15-foot side and rear setbacks. Near waterways, an ADU over 16 feet tall or 800 sq ft must meet creekside setbacks.

Design. The ADU must match the main home in color, siding or architectural features, and second-story windows, doors and balconies must be designed to limit privacy impacts on neighbors. [1][2]

Parking

The code requires one off-street space per ADU, which can be uncovered, compact, tandem or in a setback, unless the city finds tandem or setback parking isn't feasible because of site, topography or fire and life safety conditions. No space is required if:

• the ADU is 750 sq ft or less, or a studio
• it is within a half-mile walk of public transit
• it is in a historic preservation district
• it is part of the existing home or an existing accessory building
• on-street parking permits are required but not offered to the ADU's occupant
• a car-share vehicle is within one block
• it is applied for together with a new home on the lot

You must provide evidence for an exemption, such as a map showing distance to a transit stop. You don't have to replace parking lost when you convert or tear down a garage, carport or parking space. Junior ADUs never need parking. [1][2]

Fees, utilities and fire sprinklers

Impact fees. Conversions and ADUs up to 750 sq ft pay no impact fees. Larger ADUs pay a share of the full fee: 25% for 751 to 950 sq ft and 50% for 951 to 1,200 sq ft. A city staff member contacts you about application fees after you apply.

Utility connections. No new or separate utility connection or connection fee is required for an internal conversion of a house or accessory building, or for an ADU of 750 sq ft or smaller. Other new ADUs need a separate connection and pay a connection fee or capacity charge under state law and the city fee schedule. Junior ADUs never need a new connection or connection fee.

Fire sprinklers. The code says ADUs don't need sprinklers if the main home doesn't, and an ADU can't trigger sprinklers in the existing home. It does require sprinklers in structures over 1,200 sq ft of total floor area, and where remodels or additions exceed 50% of the existing floor area. The city's ADU page adds that some ADUs may need sprinklers because of fire access, hydrant distance, or being above a garage. HCD's handbook says sprinklers aren't required for an ADU if they aren't required for the main home, so ask the Fire Department's plan review division at (707) 543-3524 how these rules apply to your project.

Street dedication. If a General Plan street widening runs along your lot, you may have to dedicate right-of-way, unless a waiver is approved.

For typical costs, see our ADU cost guide. [1][2][3]

How long it takes

ADUs are approved through a building permit, without a hearing. After you apply and pay the application fees, the city has 15 business days to tell you whether the application is complete. A resubmittal gets another 15 business days. If the city misses the deadline, the application is deemed complete.

The city must approve or deny a complete application within 60 calendar days, or it is deemed approved. The clock pauses if you ask for a delay, and the city can wait to act on an ADU filed with a new house. A denial must list what's wrong and how to fix it. You can appeal an incompleteness finding or denial in writing to the Planning Commission, and the city must give a final written decision within 60 business days. A demolition permit for a detached garage being replaced by an ADU is issued at the same time as the ADU permit, with no notice or placard needed.

After final inspection, the ADU may be occupied. See our ADU permit guide. [1][2]

Garage conversions and junior ADUs

Garage conversions. Converting a legally built garage or accessory building into an ADU needs no setback, and the ADU can add 150 sq ft for a separate entrance. Conversions pay no impact fees and need no parking, and you don't have to replace the garage spaces. See our garage conversion guide.

Junior ADUs. One junior ADU is allowed per lot with a single detached home. It can be up to 500 sq ft within the walls of the house, including an attached garage, plus 150 sq ft for a separate entrance. It needs its own outside entrance and a kitchen with a sink, cooking appliance, refrigerator, counter and cabinets. It may share a bathroom with the house; if it has no inside door to the house, it needs its own bathroom.

Owner occupancy. If the junior ADU shares a bathroom, you must record a deed restriction before occupancy: the owner lives in the house or the junior ADU, and the unit can't be sold separately. This matches state law since January 1, 2026. Junior ADUs can't be rented for less than 30 days. See our junior ADU guide. [1][2][3]

Renting it out, unpermitted units and fire rebuilds

You don't have to live on the property to have an ADU. ADUs can't be rented for less than 30 days and can't be sold separately from the main home. To rent an ADU or junior ADU, it must have a stove and refrigerator. Older code text bars owner-occupancy rules only "before January 1, 2025," but the city's ADU page says owner occupancy is not required, and state law now bans owner-occupancy rules for ADUs permanently.

Unpermitted ADUs. The city can't deny a permit to legalize an ADU or junior ADU built before January 1, 2020 for code violations, unless a fix is needed for health and safety under state substandard-building rules. The city also runs an ADU Enforcement Deferral Program for some units built before March 3, 2020. Contact Planning at (707) 543-3200 to see if you qualify.

After a disaster. Under the code's Resilient City standards, if a Governor's emergency proclamation covers a hazard in Santa Rosa and your main home was substantially damaged or destroyed, a detached ADU with a permit and completed inspections can get its certificate of occupancy before the main home is rebuilt. [1][2][3]

Permit steps in Santa Rosa

1. Check your zoning

   Find your zoning district with the city's online maps (linked from the ADU page) and check for hillside, creekside or historic district rules. [1][2]

2. Prepare plans

   You need a site plan, floor plan, foundation plan, interior cross sections, construction details, elevations for new structures, a soils report and a CalGreen checklist. The Building Division has submittal checklists for new detached ADUs and for conversions and additions. [2]

3. Ask about fire sprinklers

   Check with Fire Department plan review at (707) 543-3524 whether your ADU needs sprinklers. [2]

4. Apply online

   Submit a building permit application, with each document as a separate PDF, through the city's Accela Citizen Access portal. See the Building Permits page for instructions. [2][4]

5. Pay fees and get a completeness decision

   Staff contact you about application fees. The city reviews for completeness within 15 business days of receiving the application and fees. [2]

6. Get a decision

   The city approves or denies a complete application within 60 calendar days. For a junior ADU that shares a bathroom, record the deed restriction before occupancy. [1][2]

7. Build and pass final inspection

   Schedule the final inspection through the city's automated inspection request system; after it passes, the ADU may be occupied. [2]

Who to call

• City of Santa Rosa Planning and Building

  ADU zoning and building permit questions, and the ADU Enforcement Deferral Program; planning@srcity.org, Building@srcity.org

  (707) 543-3200

  [2][4]

• Santa Rosa Fire Department Plan Review

  Fire sprinkler and fire access questions for ADUs; srfd@srcity.org

  (707) 543-3524

  [2]

Questions people ask