California ADU rules · Sonoma County
Can I Build an ADU in Santa Rosa?
Yes — you can build an ADU in Santa Rosa. California's statewide ADU law requires every city, including Santa Rosa, to approve a qualifying accessory dwelling unit by right, plus a junior ADU (JADU) on a single-family lot. What varies city to city are the local specifics below.
Can you build one?
ADUs allowed
CA state lawYes — by right
ADUs and JADUs are allowed by right in all residential and mixed-use zones; ministerial approval, no hearing.
Units on a single-family lot
CA state law1 ADU + 1 JADU
At least one ADU and one JADU per single-family lot (a conversion ADU may also be possible).
Units on a multifamily lot
CA state lawConversion ADUs (≥1, up to 25% of units) + up to 8 detached
Conversions of non-livable space (at least 1, or up to 25% of existing units) plus up to 8 detached ADUs on a lot with existing multifamily — never exceeding the number of existing units. JADUs are single-family only.
Junior ADU (JADU)
CA state lawAllowed
Up to 500 sq ft, within the walls of an existing single-family home (single-family lots only).
Size & height
Max detached ADU size
Local rule1,200 sq ft
No newly constructed detached ADU may contain more than 1,200 sq ft of habitable space — Santa Rosa's express local ceiling (matches the state default).
Max attached ADU size
CA state law50% of the primary dwelling, but ≥850 sq ft (≥1,000 sq ft for 2+ bedrooms) is always allowed
Guaranteed minimum size
CA state law800 sq ft
An 800 sq ft ADU must be allowed regardless of FAR/lot-coverage caps; a city also cannot cap an attached ADU below 850 sq ft (1,000 for 2+ bedrooms).
Max JADU size
CA state law500 sq ft
Max height
Local rule18 ft
16 ft for a one-story detached ADU; 18 ft with matching roof pitch or within ½ mi of major transit; up to 25 ft (or primary-dwelling height, whichever is lower) for an attached ADU; an absolute 27 ft for a two-story ADU or one above a garage.
Setbacks
Side setback
Local rule4 ft
4 ft side/rear for a new ADU ≤800 sq ft; an ADU above a garage must keep 5 ft side and rear. Conversions within an existing structure need no setback.
Rear setback
Local rule4 ft
4 ft rear for a new ADU ≤800 sq ft; 5 ft for an ADU above a garage. Conversions within an existing structure need no setback.
Front setback
Local ruleSame as the primary dwelling for the zone; an 800 sq ft ADU may be placed in the front yard only where no feasible alternative location exists
Separation from main house
CA state lawNone required
No statewide separation requirement between the ADU and the primary dwelling.
Parking
Parking required
CA state lawUp to 1 space
At most 1 space per ADU (or per bedroom, whichever is less) — and waived in the common cases below.
Transit parking exemption
CA state lawYes — no parking required near transit & for conversions
No parking may be required within ½ mi walking distance of transit, in a historic district, for an ADU within an existing structure, within one block of car-share, or in certain permit-parking areas.
Garage-conversion replacement parking
CA state lawNot required
When a garage/carport is demolished or converted to build an ADU, replacement parking cannot be required.
Approval, timeline & cost
Approval path
CA state lawMinisterial (by right)
No public hearing or discretionary design review for a qualifying ADU.
Approval timeline
CA state law60 days
The agency must act within 60 days of a complete application — and the ADU is deemed approved if it does not.
Owner-occupancy
CA state lawOnly for a JADU
No owner-occupancy requirement for ADUs (the prior sunset was removed). A JADU may require owner-occupancy, principally where it shares sanitation with the main house.
Impact-fee waiver
CA state lawWaived under 750 sq ft
An ADU of 750 sq ft or less pays no impact fees (the 750 sq ft threshold itself is exempt under § 66311.5); larger ADUs pay fees proportional to the primary dwelling. JADUs (≤ 500 sq ft) are exempt.
Permits required
CA state lawBuilding permit
Only a ministerial building permit — no conditional use permit or discretionary design review for a qualifying ADU.
Santa Rosa-specific factors that can change the answer
State law sets the floor, but these local conditions often decide whether a specific parcel works.
Wildland Urban Interface (WUI)
ADUs may be restricted in the Wildland Urban Interface; SB 9-style lot-split ADUs are not allowed in the WUI.
Historic districts
ADUs are allowed in historic districts but must comply with the city's historic-preservation standards; no parking may be required in a historic district.
Santa Rosa caps detached ADUs at 1,200 sq ft and otherwise tracks state limits, but adds a few local wrinkles: a 27-ft absolute ceiling for two-story or above-garage ADUs, a 5-ft (vs 4-ft) setback for above-garage units, and Wildland-Urban-Interface limits that bar SB 9 lot-split ADUs. Historic-district ADUs face added preservation standards but owe no parking.
Frequently asked questions
Can I build an ADU in Santa Rosa?
Yes. California's statewide ADU law requires Santa Rosa to approve a qualifying accessory dwelling unit ministerial (by right), plus a junior ADU (JADU) on a single-family lot.
How big can an ADU be in Santa Rosa?
A detached ADU of at least 1,200 sq ft must be allowed, and an ADU of 800 sq ft can never be zoned out by floor-area or lot-coverage limits. A JADU can be up to 500 sq ft.
What are the setback requirements for an ADU in Santa Rosa?
Side and rear setbacks are limited to 4 ft. Same as the primary dwelling for the zone; an 800 sq ft ADU may be placed in the front yard only where no feasible alternative location exists.
Is parking required for an ADU in Santa Rosa?
Up to 1 space. No parking can be required within ½ mile of transit, for conversions, or for units inside the primary home. When a garage is converted, replacement parking is not required.
How long does ADU approval take in Santa Rosa?
A complete application must be acted on within 60 days, with ministerial (by right) — no public hearing or discretionary design review for a qualifying ADU.
Do I have to live on the property to build an ADU in Santa Rosa?
Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.
Sources
- Santa Rosa Zoning Code § 20-42.130 (Accessory Dwelling Units)
- § 20-42.130(E)(3)(a)
- § 20-42.130(E)(4)
- § 20-42.130(E)(2)
- § 20-42.130(E)(2)(a)
- § 20-42.130(E)(10)(e)(1)
- § 20-42.130(E)(11)(c), (j)
- Cal. Gov. Code §§ 66310–66342 (ADU Law)
- HCD 2025 Accessory Dwelling Unit Handbook
- Cal. Gov. Code § 66317 (ministerial approval, 60-day deadline)
- Cal. Gov. Code § 66323 (by-right ADU/JADU, 800 sq ft, 4-ft setbacks)
- Cal. Gov. Code § 66333 (junior ADUs)
- Cal. Gov. Code § 66321 (size minimums & height)
- Cal. Gov. Code § 66322 (ADU parking; § 66334 covers JADU parking)
- Cal. Gov. Code § 66314 (local ordinance standards)
- Cal. Gov. Code § 66315 (owner-occupancy)
- Cal. Gov. Code § 66311.5 (impact fees: none for an ADU ≤ 750 sq ft or JADU ≤ 500 sq ft)
Last updated 2026-06-25. This is an AI-assisted summary of Santa Rosa's ADU rules, drawn from its published ordinance and California ADU law — general information, not legal advice, and it may be incomplete or out of date. Verify the controlling rule for your specific parcel with Santa Rosa Planning before relying on it.
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