Stanislaus County

Unincorporated Stanislaus County ADU rules

Research summary of local ADU rules on file for Unincorporated Stanislaus County in Stanislaus County. Not a determination for a specific lot.

Last checked October 24, 2026.

City or county ADU page

Unincorporated Stanislaus County ADU page

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Unincorporated Stanislaus County 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.

Local ADU rules
County ADU rules are in Stanislaus County Code Chapter 21.74, last amended by Ordinance CS 1408 (December 9, 2025). ADUs and JADUs are allowed in the R-1, R-2, R-3, R-A, Mixed-Use and A-2 zones (and planned developments).
Source: Stanislaus County Code Ch. 21.74 Accessory Dwellings (eCode360), § 21.74.020, accessed 2026-10-24.

Inside a city's sphere of influence
Inside a city's LAFCO-adopted sphere of influence, ADUs follow that city's applicable rules where they are consistent with state law.
Source: Stanislaus County Code Ch. 21.74 Accessory Dwellings (eCode360), § 21.74.020(A), accessed 2026-10-24.

Duplex and multifamily parcels
Duplex: one JADU and two detached ADUs. Multifamily: converted ADUs in non-livable space up to 25% of units, plus one detached ADU per existing multifamily dwelling up to 8 per parcel, or up to 2 with a proposed multifamily building.
Source: Stanislaus County Code Ch. 21.74 Accessory Dwellings (eCode360), § 21.74.030(A)(2)-(3), accessed 2026-10-24.

A-2 agricultural parcels
On A-2 parcels of 20 acres or more with one home, one ADU is allowed in place of a second dwelling, plus one JADU. An A-2 ADU must be within 150 ft of the main home and not displace crop land, unless a staff “approval” permit allows another spot.
Source: Stanislaus County Code Ch. 21.74 Accessory Dwellings (eCode360), § 21.74.030(A)(4)(c), (C)(1), accessed 2026-10-24.

Size
A new ADU may be up to 1,200 sq ft of living space; a JADU up to 500 sq ft. A mobile home may be used as a detached ADU if it meets the chapter.
Source: Stanislaus County Code Ch. 21.74 Accessory Dwellings (eCode360), § 21.74.030(B), (D), accessed 2026-10-24.

Height and setbacks
ADU height follows the limit for homes in the zone. New construction needs at least 4 ft side and rear setbacks; converting an existing legal garage or accessory building needs no added setback.
Source: Stanislaus County Code Ch. 21.74 Accessory Dwellings (eCode360), § 21.74.040(A)-(B), accessed 2026-10-24.

Parking
One space per ADU, except none for a converted garage or accessory structure, within a half mile of a public transit stop, where on-street permits are not offered to the occupant, within one block of car share, or for a JADU.
Source: Stanislaus County Code Ch. 21.74 Accessory Dwellings (eCode360), § 21.74.040(C), accessed 2026-10-24.

Density and lot coverage
A conforming ADU does not count toward density, and lot coverage limits do not apply to ADUs.
Source: Stanislaus County Code Ch. 21.74 Accessory Dwellings (eCode360), § 21.74.040(D)-(E), accessed 2026-10-24.

Rentals
ADUs and JADUs may be rented only for terms longer than 30 days and may not be sold separately from the parcel except as state law allows.
Source: Stanislaus County Code Ch. 21.74 Accessory Dwellings (eCode360), § 21.74.050(A), (C), accessed 2026-10-24.

Water, septic and fire
ADUs must meet local and state water supply and wastewater rules, County Fire Code and Public Works access standards, and current Fire Code standards in high and very high fire hazard severity zones.
Source: Stanislaus County Code Ch. 21.74 Accessory Dwellings (eCode360), § 21.74.030(E)-(G), accessed 2026-10-24.

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 Unincorporated Stanislaus County?

State law sets a baseline for ADUs in Unincorporated Stanislaus County, 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 Stanislaus County Planning and Community Development Department, or run a free address summary.

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