Everything homeowners need to know about building an accessory dwelling unit in Santa Rosa - size limits, setbacks, permits, and how the city's post-wildfire push to speed up ADU permitting still shapes the process today.
Last verified: August 2026
8/10 · Very ADU-friendly
1,200 sq ft*
Max ADU size
16-18 ft*
Max height
Not required
Owner-occupancy
By-right
Permit type
This page summarizes California's statewide ADU law and Santa Rosa's local standards (Municipal Code Chapter 20-42) for general reference - it is not legal advice. Regulations change; always confirm current requirements with the Santa Rosa Planning & Economic Development Department before designing or applying for permits. See sources below.
Zoning & size requirements
What you're allowed to build
ADU type
Max size
Max height
Notes
Detached (new build or garage conversion)
1,200 sq ft under California state law
16 ft for a single-story unit; two-story detached ADUs are permitted in some circumstances at greater height
4 ft side and rear setbacks for new construction; a conversion of an existing legally-built structure is generally exempt from these setbacks
50% of the primary dwelling's living area or 1,200 sq ft, whichever is smaller; state law guarantees at least an 800 sq ft ADU regardless of other site limits
Generally follows the underlying zoning district's height standard
Common approach for garage conversions or above-garage additions; JADUs cap at 500 sq ft
Allowed zoning districts
Single-family and multifamily residential zones citywide. On lots in the Coffey Park and Fountaingrove areas that were destroyed by the 2017 Tubbs Fire, the city allows a detached ADU to be built and occupied before the primary home is rebuilt, so owners can live on site during reconstruction - confirm current requirements for water and sewer or septic capacity with Planning & Economic Development.
Additional standards
Setbacks, parking & other rules
Setbacks
4 ft from interior side and rear property lines for new construction; front and street-side setbacks generally follow the underlying zone and may be greater than 4 ft; conversions of existing structures are generally exempt
Parking
One space is typically required, but waived for ADUs of 750 sq ft or less, units within existing structures, historic districts, near transit, on streets without on-street parking permits available to the unit, or near a car-share vehicle
Units per lot
Up to one ADU and one JADU permitted on a single-family lot under state law; qualifying multifamily properties can add up to eight detached ADUs under a 2024 state law change (SB 1211)
Owner-occupancy
Not required for a standard ADU statewide since 2024 (AB 976). A JADU generally still requires the owner to occupy either the primary home or the JADU
Building code
Must meet the California Residential Code and CalGreen standards as locally adopted; a CalGreen checklist is part of the standard submittal
Rental license
ADUs and JADUs cannot be used as short-term rentals of 30 days or less under the city's short-term rental ordinance; existing ADUs with an active short-term rental permit issued before the restriction may continue until they fall out of compliance
Ordinance history
How Santa Rosa's ADU rules got here
2017Statewide by-right ADU approval begins. California law requires cities to ministerially approve qualifying ADU applications, without discretionary review or a conditional use permit.
2017The Tubbs Fire reshapes local housing policy. The October 2017 Tubbs Fire destroyed thousands of homes in the Coffey Park and Fountaingrove neighborhoods. In the years that followed, Santa Rosa restructured its ADU program with reduced or waived fees for smaller units and faster review, and adopted rules letting property owners build and occupy a detached ADU on a fire-damaged lot before rebuilding the primary home.
2020State law tightens further. A package of bills (AB 68, AB 881, AB 587, AB 2299, AB 671) shrinks what cities can restrict and expands by-right approval statewide.
2024Owner-occupancy eliminated; multifamily ADUs expanded. AB 976 permanently bars California cities from requiring owner-occupancy for standard ADUs; SB 1211 lets qualifying multifamily properties add up to eight detached ADUs.
2025State finds Sonoma County's separate ordinance noncompliant. In a January 2025 letter, HCD found the ADU ordinance covering unincorporated Sonoma County - a different jurisdiction from the City of Santa Rosa, which has its own ordinance and permitting department - did not comply with state ADU law. No comparable non-compliance letter specific to the City of Santa Rosa's own ordinance was found in available public records as of this writing.
Santa Rosa's fee-reduction and expedited-review approach, adopted in the wake of the Tubbs Fire, has generally carried forward into the city's standard ADU program rather than staying limited to fire rebuilds - one reason the city's ADU rules read as more homeowner-friendly than many California peers.
Permit process
How Santa Rosa ADU permitting works
1
Pre-application check
Confirm your zoning district and, if your lot was affected by wildfire, your options for building an ADU before the primary home is rebuilt.
2
Prepare your plan set
You'll need a site plan, floor plan, foundation plan, sections, details, elevations, a soils report, and a CalGreen checklist.
3
Submit to the Building Division
The city reviews submittals for completeness within 15 business days of filing.
4
Plan review & decision
The city issues a decision within 60 calendar days of a complete submittal, consistent with the state law maximum.
5
Building permit & construction
Once approved, pull your building permit and begin construction, scheduling standard framing, plumbing, electrical, and other inspections along the way.
6
Final inspection & occupancy
Schedule your final inspection; the ADU can be occupied once it passes.
The Planning Division can be reached at (707) 543-3200 for zoning questions; confirm current fee schedules and submittal checklists with Planning & Economic Development before you apply.
Budgeting
What it costs to build an ADU in Santa Rosa
Garage conversion
Roughly $65,000-$180,000, the least expensive path since the shell and foundation already exist
New detached ADU
Roughly $140,000-$330,000+ for a fully built freestanding unit, depending on size, finishes, and site conditions
Attached addition / above-garage unit
Costs vary widely depending on whether it's new construction over an existing garage or an addition to the primary home; get multiple contractor bids
Impact fees
Waived for ADUs of 750 sq ft or less and for conversion ADUs; units from 751-950 sq ft pay 25% of standard impact fees, and units from 951-1,200 sq ft pay 50%
Utility connection fees
Waived for internal conversions under 750 sq ft; larger or detached units may require separate utility connections - confirm with Planning & Economic Development
These are general ranges from local contractor estimates and regional reporting, not quotes - actual cost depends heavily on lot conditions, finishes, and whether utilities need to be extended or upsized.
Before you apply
Tips for a smoother approval
Keep your unit at or under 750 sq ft if cost is the priority. That threshold clears both impact fees and utility connection fees for internal conversions - a meaningful savings compared with a larger unit.
If you're rebuilding after wildfire damage, ask about building the ADU first. Santa Rosa allows a detached ADU to be built and occupied on a fire-damaged lot before the primary home is rebuilt, letting you live on site during construction.
Bring a complete submittal the first time. The city reviews for completeness within 15 business days, but an incomplete package resets your place in line.
Check whether you qualify for a parking exemption. Units of 750 sq ft or less, conversions, and units near transit or in historic districts typically don't need a dedicated parking space.
If you have an unpermitted existing ADU, ask about the deferral program. Units built before March 3, 2020 may qualify for a multi-year enforcement deferral while you bring them up to code - don't assume you need to demolish first.
FAQ
Common questions
Do I need to live on the property to build an ADU in Santa Rosa?
No. California eliminated owner-occupancy requirements for standard ADUs statewide in 2024 (AB 976). A junior ADU (JADU) generally still requires the owner to occupy either the primary home or the JADU.
How many ADUs can I build on one lot?
One ADU plus one JADU on a single-family lot under state law. Qualifying multifamily properties can add up to eight detached ADUs under a 2024 state law change (SB 1211).
Do I need extra parking for an ADU?
Often not. Parking is waived for ADUs of 750 sq ft or less, conversions of existing space, units in historic districts, units near transit, and a few other categories.
How long does the permit process take?
The city reviews for completeness within 15 business days and issues a decision within 60 calendar days of a complete submittal, consistent with the state law maximum.
What's the maximum size for a detached ADU?
Up to 1,200 sq ft, with a 16 ft height limit for a single-story unit and 4 ft side and rear setbacks for new construction.
Can I build an ADU on my property before rebuilding my fire-damaged home?
Yes, in most cases. Santa Rosa allows a detached ADU to be built and occupied on a lot before the primary home is rebuilt, as long as adequate water and sewer or septic capacity can be demonstrated - a policy that grew out of the rebuilding effort after the 2017 Tubbs Fire.
What if I already built an ADU without a permit?
Santa Rosa has offered a multi-year enforcement deferral for unpermitted ADUs built before March 3, 2020, giving owners time to bring the unit up to code rather than facing immediate enforcement. Confirm current program status and eligibility with Planning & Economic Development.
How much does an ADU cost to build in Santa Rosa?
Garage conversions tend to run roughly $65,000-$180,000, and new detached units commonly run $140,000-$330,000 or more, based on local contractor estimates and regional reporting - not counting permit fees. Impact fees are waived under 750 sq ft and reduced up to 1,200 sq ft.
Can I rent my ADU out on Airbnb or a short-term rental platform?
No, not for new permits. Santa Rosa doesn't allow ADUs or JADUs to be used as short-term rentals of 30 days or less; a limited number of existing ADUs with an active short-term rental permit issued before the restriction may continue operating until they fall out of compliance.
