Sonoma County
Town of Windsor ADU rules
Research summary of local ADU rules on file for Town of Windsor in Sonoma County. Not a determination for a specific lot.
City or county ADU page
Check any California address for freeTown of Windsor 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 Town's Zoning Code standards (a § 66314 unit). The 800 sq ft detached ADU can be in the front setback.
Source: Town of Windsor Accessory Dwelling Units page, 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. Plus one attached ADU under Gov. Code § 66314.
Source: Town of Windsor Accessory Dwelling Units page, What can I build?, accessed 2026-10-23.
Setbacks and height
Rear and side setbacks are typically at least 4 ft. Height is 16 ft, with exceptions in the Zoning Code. ADUs with two or more bedrooms may be up to 1,200 sq ft, and attached ADUs generally have architectural and design standards.
Source: Town of Windsor Accessory Dwelling Units page, What are the development standards, accessed 2026-10-23.
Rentals and owner occupancy
ADUs and JADUs cannot be short-term rentals. For a JADU without its own bathroom, the owner must live on site, and a JADU deed restriction must be recorded.
Source: Town of Windsor Accessory Dwelling Units page, Are there any restricted uses of ADUs?, accessed 2026-10-23.
Unpermitted pre-2020 units
State law requires permits for certain ADUs and JADUs built before January 1, 2020 and removes financial penalties for owners who legalize them (AB 2533). Contact adu@townofwindsor.ca.gov.
Source: Town of Windsor Accessory Dwelling Units page, Does the Town have an Amnesty ADU Program, accessed 2026-10-23.
Town ADU Planner
Call 707-838-5337 or email adu@townofwindsor.ca.gov. Counter hours at Town Hall, Building 400: Tuesdays 11:30 am–12 pm and 3–4 pm; other times by appointment, Monday–Thursday.
Source: Town of Windsor Accessory Dwelling Units page, Town Staff ADU Planning Hours, 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 Town of Windsor?
State law sets a baseline for ADUs in Town of Windsor, 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 Town of Windsor Community Development Department, or run a free address summary.
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