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Rancho Santa Margarita ADU rules

Research summary of what we found for City of Rancho Santa Margarita in Orange County. Not a determination for a specific lot.

City or county ADU page

Rancho Santa Margarita Planning department. No ADU-specific page was found.

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How big can an ADU be in Rancho Santa Margarita?

Maximum size

A detached ADU may be up to 1,200 sq ft. An attached ADU may be up to 1,200 sq ft or 50% of the main home's floor area, whichever is less, but never below 800 sq ft. A converted ADU that does not add floor area has no size limit, and one in an accessory structure may add up to 150 sq ft for entry and exit. Every ADU must be at least 150 sq ft. Floor area, lot coverage, open space or front setback rules are waived as needed to allow an 800 sq ft ADU.

Source: Rancho Santa Margarita Zoning Code § 9.04.190 Accessory dwelling units and junior accessory dwelling units (Municode), § 9.04.190(e)(4)(a)-(b), (e)(5), accessed 2026-11-03.

ADU setbacks in Rancho Santa Margarita

Setbacks

New attached and detached ADUs need at least 4 ft from the side and rear lot lines, and the same front setback as other buildings on the lot (waived as needed to allow an 800 sq ft ADU). Converted ADUs need no setback if the existing structure's side and rear setbacks are enough for fire and safety, as the City's building staff decides.

Source: Rancho Santa Margarita Zoning Code § 9.04.190 Accessory dwelling units and junior accessory dwelling units (Municode), § 9.04.190(e)(5)-(6), accessed 2026-11-03.

What we found for Rancho Santa Margarita

What we have for this place. Where a local figure is stricter than the California state baseline, both are shown.

Local ADU rules

Rancho Santa Margarita's ADU rules are in Zoning Code section 9.04.190, last amended by Ordinance 25-03 (October 8, 2025). ADU and JADU applications are acted on ministerially, without discretionary review or a hearing, within the time state law sets. The ADU types listed in Gov. Code § 66323 are not held to local standards such as front setbacks, size limits or parking.

Source: Rancho Santa Margarita Zoning Code § 9.04.190 Accessory dwelling units and junior accessory dwelling units (Municode), § 9.04.190(h)(3), (h)(6), accessed 2026-11-03.

Number of ADUs

On a lot with a single-family home: one attached or converted ADU and one JADU, plus one new detached ADU with 4 ft side and rear setbacks. On a lot with an existing multifamily building: converted ADUs in non-livable space (at least one, up to 25% of the existing units) and up to 8 detached ADUs, not more than the number of existing units. On a lot with a proposed multifamily building: up to 2 detached ADUs.

Source: Rancho Santa Margarita Zoning Code § 9.04.190 Accessory dwelling units and junior accessory dwelling units (Municode), § 9.04.190(e)(3), accessed 2026-11-03.

Height

A detached ADU may be 16 ft. It may be 18 ft within a half mile walk of a major transit stop or high-quality transit corridor (up to 20 ft to align with the main home's roof pitch), or on a lot with a multistory multifamily building. An attached ADU may be as tall as the zone's limit for the main home or 25 ft, whichever is lower, and no more than two stories.

Source: Rancho Santa Margarita Zoning Code § 9.04.190 Accessory dwelling units and junior accessory dwelling units (Municode), § 9.04.190(e)(4)(c), accessed 2026-11-03.

Parking

One off-street space for an attached or detached ADU, which may be in a setback or tandem on a driveway unless the Director finds site, slope or fire safety reasons against it. No space is needed within a half mile walk of public transit, in a historic district, for a converted ADU, where on-street permits are required but not offered, within one block of a car share station, or when the ADU is filed with a new home or multifamily building. Garage, carport or other parking spaces removed for an ADU do not have to be replaced. The state-law ADU types and JADUs need no added parking.

Source: Rancho Santa Margarita Zoning Code § 9.04.190 Accessory dwelling units and junior accessory dwelling units (Municode), § 9.04.190(e)(7), (f)(6), (h)(6), accessed 2026-11-03.

Junior ADUs

A JADU of 150 to 500 sq ft is allowed inside the walls of a single-family home (an existing attached garage counts), with its own entrance and an efficiency kitchen. If it shares a bathroom, it needs an inside door to the main living area. It uses the home's utility connections and may not have its own meter. A deed restriction must be recorded before the building permit is issued.

Source: Rancho Santa Margarita Zoning Code § 9.04.190 Accessory dwelling units and junior accessory dwelling units (Municode), § 9.04.190(f), (i)(2), accessed 2026-11-03.

Fees, utilities and renting

No impact fee for an ADU under 750 sq ft; larger ADUs pay in proportion to the main home's size. An ADU may use the main home's utility connections unless the law, the utility or the Public Works Director requires otherwise. Fire sprinklers are needed only if the main home needs them. An ADU may be rented but not for 30 days or less, and may not be sold separately except as state law allows. The owner does not have to live on a lot with an ADU.

Source: Rancho Santa Margarita Zoning Code § 9.04.190 Accessory dwelling units and junior accessory dwelling units (Municode), § 9.04.190(g)(1)-(3)(a), (h)(1), (i)(1), (j), accessed 2026-11-03.

State housing department (HCD) review

On October 11, 2024, HCD found that Rancho Santa Margarita's earlier ADU ordinance (Ordinance 23-01, April 2023) did not comply with state ADU law on outdated code references, limits on combining ADU types, a size cap on a detached ADU paired with a JADU, a missing parking exemption, a JADU rental term and replacement parking for garage JADUs. The City had until November 10, 2024 to respond. It adopted Ordinance 25-03 in October 2025, which changed these sections. Confirm the current rules with the City of Rancho Santa Margarita.

Source: HCD ordinance review letter, City of Rancho Santa Margarita, Letter of October 11, 2024, accessed 2026-11-03.

California state rules

The statewide baseline recorded from state law and the HCD ADU Handbook.

Detached size cap described in state law

1,200 sq ft. 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. 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, 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, 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. 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. 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. 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. What we have 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.

Starting January 1, 2027: two detached ADUs

Starting January 1, 2027, AB 956 (Chapter 791, Statutes of 2026) raises from one to two the number of new detached ADUs a city or county must allow, without discretionary review, on a lot with a proposed or existing single-family home (Gov. Code 66323(a)). Each may be held to 800 sq ft, 4 ft side and rear setbacks and the state height limits. The city or county does not have to also allow a JADU on a lot where two new detached ADUs have been built. AB 956 also makes HOA and deed rules that effectively prohibit or unreasonably restrict an ADU or JADU void on any lot zoned to allow a single-family home, not only lots zoned for single-family use (Civil Code 4751 and 714.3).

Source: AB 956 (2025-2026), Chapter 791, Statutes of 2026, Gov. Code 66323; Civil Code 714.3, 4751; signed September 29, 2026, accessed 2026-11-03.

Starting January 1, 2027: impact fees above 750 sq ft

No impact fee may be charged on an ADU of 750 sq ft or less, or a JADU of 500 sq ft or less (Gov. Code 66311.5(c)). Starting January 1, 2027, SB 1117 (Chapter 809, Statutes of 2026) changes how fees are figured for larger ADUs: for up to two ADUs on a lot, the proportional impact fee is charged only on the interior livable space above 750 sq ft. On a lot with more than two ADUs, the fee stays proportional to the whole ADU. Utility connection fees and capacity charges are not changed.

Source: SB 1117 (2025-2026), Chapter 809, Statutes of 2026, Gov. Code 66311.5(c); signed September 29, 2026, accessed 2026-11-03.

State baseline on the directory → · State ADU rules on the homepage →

ADU rules near Rancho Santa Margarita

Can I build an ADU in Rancho Santa Margarita?

State law sets a baseline for ADUs in Rancho Santa Margarita, and what we found locally is 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 Rancho Santa Margarita Development Services Department (Planning Division), or run a free address summary.

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