Orange County

Westminster ADU rules

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

Last checked October 23, 2026.

City or county ADU page

Westminster 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.

Permit route
Projects that only involve an ADU and/or junior ADU go through a combined Planning Division Zoning Clearance and Building Division plan check. Plans and application materials are submitted to the Building Division, in person or online through the Westminster Build Online Portal.
Source: City of Westminster, Accessory Dwelling Units page, How to Apply: The Process, accessed 2026-10-23.

Steps
1) Consult and design (Planning, Building and Engineering Divisions each review ADUs); 2) prepare construction plans and submittal documents; 3) formal review; 4) building permit issued once all agencies sign off, with inspections during construction.
Source: City of Westminster, Accessory Dwelling Units page, How to Apply: Steps 1 to 4, accessed 2026-10-23.

Projects needing a Development Review first
New residential projects with four or more new units need a Development Review by the Planning Division before building plan check. An ADU with a new or expanded multiple-family residence, or one adding impervious surface to a multifamily property with a prior Water Quality Management Plan, needs a separate Development Review or Zoning Clearance before plan check.
Source: City of Westminster, PL-117 Accessory Dwelling Unit Application (plan check and zoning clearance submittal requirements), Projects That Do Not Qualify for Combined Zoning Clearance and Plan Check, accessed 2026-10-23.

What to submit
Signed application form, ADU Housing Questionnaire, address request form (if a new address is requested), grant deed (junior ADU only), dimensioned site, floor and roof plans and elevations, construction plans (framing, utility plan, sections, Title 24, CALGreen), precise grading and erosion control plans, and a separate site plan showing all existing and proposed water meters.
Source: City of Westminster, PL-117 Accessory Dwelling Unit Application (plan check and zoning clearance submittal requirements), Minimum Submittal Requirements, accessed 2026-10-23.

Easements
Plans must show all easements on the property, or note that there are none. No structure, including roof eaves, may be built in an easement unless the easement holder agrees; a preliminary title report can confirm easements.
Source: City of Westminster, PL-117 Accessory Dwelling Unit Application (plan check and zoning clearance submittal requirements), Easements, accessed 2026-10-23.

Flood zones
The owner must check whether the property is in a FEMA Special Flood Hazard Area; property in one is subject to flood zone requirements (contact the Engineering Division).
Source: City of Westminster, PL-117 Accessory Dwelling Unit Application (plan check and zoning clearance submittal requirements), Important Notes: Checking Flood Zones, accessed 2026-10-23.

Fire sprinklers
Fire sprinklers are not required in an ADU or junior ADU unless they are required for the primary residence.
Source: City of Westminster, PL-117 Accessory Dwelling Unit Application (plan check and zoning clearance submittal requirements), Important Notes: Fire Sprinklers, accessed 2026-10-23.

Rentals
No short-term rental (30 days or less) of an ADU or junior ADU.
Source: City of Westminster, PL-117 Accessory Dwelling Unit Application (plan check and zoning clearance submittal requirements), Important Notes: Short Term Rental, accessed 2026-10-23.

Junior ADU utilities
A junior ADU uses the same water, sewer and other utility connections as the main home; no separate meter is allowed for it.
Source: City of Westminster, PL-117 Accessory Dwelling Unit Application (plan check and zoning clearance submittal requirements), Important Notes: JADU Utilities, accessed 2026-10-23.

Separate permits
Solar panels, fire sprinklers (Orange County Fire Authority), fences, retaining walls, grading, demolition and work in the public right-of-way each need their own permit.
Source: City of Westminster, PL-117 Accessory Dwelling Unit Application (plan check and zoning clearance submittal requirements), Important Notes, accessed 2026-10-23.

Who to contact
Planning Division (714) 548-3247, planning@westminster-ca.gov; Development Engineering (714) 548-3465; Building Division (714) 548-3248.
Source: City of Westminster, Accessory Dwelling Units page, Contact Information, 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 Westminster?

State law sets a baseline for ADUs in Westminster, 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 Westminster Community Development Department (Planning Division), or run a free address summary.

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