Sonoma County
Santa Rosa ADU rules
Research summary of local ADU rules on file for City of Santa Rosa in Sonoma County. Not a determination for a specific lot.
City or county ADU page
Check any California address for freeCity of Santa Rosa rules on file
Local rules recorded in this project for this jurisdiction. Where a city figure on file is stricter than the state baseline on file, both are shown.
What “you can build” on a single-family lot
One converted ADU, one JADU and one new detached ADU of up to 800 sq ft (Gov. Code § 66323 units), plus one ADU built under the City's Zoning Code standards (a § 66314 unit). The 800 sq ft detached ADU can be in the front setback.
Source: City of Santa Rosa Accessory Dwelling Units page, Start Here: What Can I Build?, accessed 2026-10-23.
Multifamily lots
Converted ADUs: up to 25% of existing units (at least one). Detached ADUs: up to 2 with new multifamily, or up to 8 with existing multifamily but not more than the existing unit count. Attached ADUs: up to 2.
Source: City of Santa Rosa Accessory Dwelling Units page, Start Here: What Can I Build?, accessed 2026-10-23.
Setbacks for Zoning Code ADUs
Side and rear setbacks are typically 4 ft and corner side 8 ft (may differ in Hillside areas). Front setbacks generally follow the zone, but building in the front setback is allowed if it would otherwise block an 800 sq ft ADU or there is no other place on the lot.
Source: City of Santa Rosa Accessory Dwelling Units page, Single-Family Zoning District Development Standards for ADUs, accessed 2026-10-23.
Detached ADU height
Detached ADUs: 16 ft for one story and 27 ft for two stories (see the Zoning Code for exceptions). Lot coverage limits cannot block an 800 sq ft ADU.
Source: City of Santa Rosa Accessory Dwelling Units page, Single-Family Zoning District Development Standards for ADUs, accessed 2026-10-23.
Parking
One space may be required for some new detached ADUs, but none is needed for an ADU of 750 sq ft or less, within an existing structure, near transit or car share, in a historic district, or where on-street permits are not available. JADUs and conversion ADUs need no parking.
Source: City of Santa Rosa Accessory Dwelling Units page, Parking Requirements, accessed 2026-10-23.
How to apply and timelines
ADUs go through a Building Permit. The City checks completeness within 15 business days and decides within 60 calendar days of a complete submittal; incomplete findings and denials can be appealed in writing to the Planning Commission.
Source: City of Santa Rosa Accessory Dwelling Units page, How to Apply, accessed 2026-10-23.
Impact fees
No impact fees for ADUs under 750 sq ft or conversion ADUs; reduced fees may apply to larger ADUs.
Source: City of Santa Rosa Accessory Dwelling Units page, Costs and Fees, accessed 2026-10-23.
Fire sprinklers
Some ADUs need fire sprinklers depending on fire access, hydrant distance or a location above a garage; check with Santa Rosa Fire Plan Review at (707) 543-3524 or srfd@srcity.org.
Source: City of Santa Rosa Accessory Dwelling Units page, Fire and Building Requirements, accessed 2026-10-23.
Enforcement deferral for older unpermitted ADUs
Owners of an unpermitted ADU built before March 3, 2020 may be able to get a 5-year deferral on enforcement while they legalize it. Contact Planning: planning@srcity.org or (707) 543-3200.
Source: City of Santa Rosa Accessory Dwelling Units page, Existing Unpermitted ADUs, accessed 2026-10-23.
California state rules on file
The statewide baseline recorded from state law and the HCD ADU Handbook.
Detached size cap described in state law
1,200 sq ft. Recorded in this rules file from Government Code section 66314.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.
Side and rear setback cap for a new ADU
4 ft. Recorded in this rules file from Government Code section 66314, which describes a cap on side and rear setbacks for a new ADU.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.
Setback for a conversion of an existing structure
No additional setback, as recorded in this rules file from Government Code section 66314 for a conversion of an existing structure.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.
Minimum lot size
A city may not impose a minimum lot size for an ADU, as recorded in this rules file from Government Code section 66314.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.
Minimum unit the handbook says cities must allow
At least an 800 sq ft ADU with 4 ft side and rear setbacks. The HCD ADU Handbook (updated March 2026) describes this under section 66321(b)(3).
Source: HCD ADU Handbook, 66321(b)(3); handbook updated March 2026, accessed 2026-10-16.
Detached height described in the handbook
16 ft, or 18 ft or 20 ft in some cases. The HCD ADU Handbook (updated March 2026) describes this under section 66321(b)(4).
Source: HCD ADU Handbook, 66321(b)(4); handbook updated March 2026, accessed 2026-10-16.
Permit decision deadline
60 days. Recorded in this rules file from Government Code section 66317(a)(3): the permitting agency must decide on (approve or deny) a completed ADU application within 60 days when an existing single-family or multifamily dwelling is on the lot. Section 66317(a)(1) says the application is considered ministerially, without discretionary review or a hearing.
Source: California Government Code section 66317, 66317(a)(1), (a)(3), accessed 2026-10-17.
Owner-occupancy requirement
None. Recorded in this rules file from Government Code section 66315: a local agency may not impose an owner-occupancy requirement on an ADU. It may require that the property be used for rentals of terms 30 days or longer. The HCD ADU Handbook (updated March 2026) describes the same rule.
Source: California Government Code section 66315, 66315; HCD ADU Handbook updated March 2026, accessed 2026-10-17.
Parking near public transit
No parking standards within one-half mile walking distance of public transit. Recorded in this rules file from Government Code section 66322(a)(1). Section 66322(a) lists several other cases where parking standards may not be imposed.
Source: California Government Code section 66322, 66322(a), accessed 2026-10-17.
Ministerial categories
The HCD ADU Handbook (updated March 2026) states that Government Code section 66323 sets four ministerial categories. This rules file does not restate those four categories.
Source: HCD ADU Handbook, 66323; handbook updated March 2026, accessed 2026-10-16.
Fire Hazard Severity Zones
If your lot is in a Fire Hazard Severity Zone, the CAL FIRE Office of the State Fire Marshal says in Information Bulletin 25-004 (issued March 3, 2025): “Fire Hazard Severity Zones (FHSZs) should not restrict the development of Accessory Dwelling Units (ADUs). However, additional building standards may be necessary, including but not limited to California Fire Code Chapter 49 and California Building Code Chapter 7A.” State ADU law does not itself bar an ADU there. A city or county may still apply its building code, including wildfire-resistant construction (Gov. Code 66314(d)(8)); require side and rear setbacks “sufficient for fire and safety” for a unit converted under 66323(a)(1); and decline parking in setbacks on specific fire and life safety findings (66314(d)(10)(B)). It may also consider public safety when it designates where ADUs may be permitted (66314(a)). Sprinklers can't be required in an ADU or JADU if the primary residence doesn't need them (66314(d)(12), 66323(d)). Some cities and counties still apply their own fire-zone limits. Where this summary has one, it is listed with the local rules. This summary does not look up your lot. Check the CAL FIRE Fire Hazard Severity Zone map viewer linked from the State Fire Marshal's Fire Hazard Severity Zones page: https://experience.arcgis.com/experience/5065c998b4b0462f9ec3c6c226c610a9
Source: CAL FIRE Office of the State Fire Marshal Information Bulletin 25-004, page 4, issued March 3, 2025; Gov. Code 66314, 66323, accessed 2026-10-20.
State baseline on the directory → · State ADU rules on the homepage →
Can I build an ADU in Santa Rosa?
State law sets a baseline for ADUs in Santa Rosa, and the local standards on file are listed on this page. Whether a specific lot can add an ADU depends on zoning, utilities, and other site facts this page does not measure. Confirm with the City of Santa Rosa Planning and Economic Development Department, or run a free address summary.
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