Contra Costa County

Oakley ADU rules

Research summary of local ADU rules on file for Oakley in Contra Costa County. Not a determination for a specific lot.

Last checked October 26, 2026.

City or county ADU page

Oakley 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.

Which rules apply
Oakley's ADU section (Municipal Code Sec. 9.1.1102, last amended by Ordinance 8-26 on May 12, 2026) follows state ADU law (Gov. Code 66310-66342) and adds a few local standards. Its size cap for attached ADUs is left out of this summary because it may conflict with state law; state rules apply to that item and to everything the section does not cover.
Source: Oakley Municipal Code Sec. 9.1.1102 Accessory Dwelling Units (eCode360; as amended by Ord. 8-26, May 12, 2026), Sec. 9.1.1102(a)-(b), accessed 2026-10-25.

State law controls
If any part of the section conflicts with state ADU law, state law governs, and unclear parts are read to match state law.
Source: Oakley Municipal Code Sec. 9.1.1102 Accessory Dwelling Units (eCode360; as amended by Ord. 8-26, May 12, 2026), Sec. 9.1.1102(b)(2)-(3), accessed 2026-10-25.

Detached ADU size
For ADUs not covered by Gov. Code 66323: up to 850 sq ft for one bedroom or less, up to 1,000 sq ft for more than one bedroom, and up to 1,200 sq ft with more than one bedroom on estate lots (P-1, R-15, R-20, R-40 or AL zones, at least 15,000 sq ft). The 850 sq ft limit also applies when the ADU would bring total lot coverage to 50% or more.
Source: Oakley Municipal Code Sec. 9.1.1102 Accessory Dwelling Units (eCode360; as amended by Ord. 8-26, May 12, 2026), Sec. 9.1.1102(c)(1)(a), accessed 2026-10-25.

Garage attached to a detached ADU
Up to 225 sq ft on any lot where an ADU is allowed, or up to 450 sq ft on estate lots (R-15, R-20, R-40 or AL zones, at least 15,000 sq ft).
Source: Oakley Municipal Code Sec. 9.1.1102 Accessory Dwelling Units (eCode360; as amended by Ord. 8-26, May 12, 2026), Sec. 9.1.1102(c)(2), accessed 2026-10-25.

Short-term rentals
No ADU or junior ADU may be rented for less than 30 consecutive days.
Source: Oakley Municipal Code Sec. 9.1.1102 Accessory Dwelling Units (eCode360; as amended by Ord. 8-26, May 12, 2026), Sec. 9.1.1102(c)(3), accessed 2026-10-25.

Where to ask
Oakley Planning Division. The City's ADU and junior ADU page has its ADU information.
Source: City of Oakley, ADUs/Junior ADUs page, accessed 2026-10-25.

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 Oakley?

State law sets a baseline for ADUs in Oakley, 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 Oakley Planning Division, or run a free address summary.

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