California ADU rules · Los Angeles County
Can I Build an ADU in San Marino?
Yes — you can build an ADU in San Marino. California's statewide ADU law requires every city, including San Marino, to approve a qualifying accessory dwelling unit by right, plus a junior ADU (JADU) on a single-family lot. What varies city to city are the local specifics below.
Can you build one?
ADUs allowed
CA state lawYes — by right
ADUs and JADUs are allowed by right in all residential and mixed-use zones; ministerial approval, no hearing.
Units on a single-family lot
Local rule1 detached ADU + 1 JADU + 1 conversion ADU (if site allows)
Allows up to 3 units (1 detached ADU, 1 JADU, 1 conversion ADU) on a single-family lot if site conditions permit.
Units on a multifamily lot
Local ruleconversions (>=1 or 25% of units) + up to 8 detached (not to exceed number of existing units)
Detached ADUs on multifamily lots capped at number of existing units, up to 8.
Junior ADU (JADU)
CA state lawAllowed
Up to 500 sq ft, within the walls of an existing single-family home (single-family lots only).
Size & height
Max detached ADU size
Local rule1,200 sq ft
Local maximum matches state cap; explicitly stated.
Max attached ADU size
Local ruleUp to 50% of primary dwelling, min 150 sq ft, max 1,200 sq ft
Local rule sets explicit min and max for attached ADUs.
Guaranteed minimum size
CA state law800 sq ft
An 800 sq ft ADU must be allowed regardless of FAR/lot-coverage caps; a city also cannot cap an attached ADU below 850 sq ft (1,000 for 2+ bedrooms).
Max JADU size
CA state law500 sq ft
Max height
Local rule16 ft
Detached ADUs limited to 16 ft and 1 story; attached ADUs may be taller (see local code).
Setbacks
Side setback
CA state law4 ft
A city cannot require more than 4 ft side or rear setback; conversions of existing structures are exempt.
Rear setback
CA state law4 ft
Front setback
CA state lawNo front setback may block the mandatory 800 sq ft / 16-ft / 4-ft-setback ADU; otherwise per base zone
Separation from main house
Local rule6 ft
Detached ADUs must be at least 6 ft from primary dwelling and other structures.
Parking
Parking required
Local ruleUp to 1 space
1 off-street space per ADU unless exempt; exemptions mirror state law.
Transit parking exemption
CA state lawYes — no parking required near transit & for conversions
No parking may be required within ½ mi walking distance of transit, in a historic district, for an ADU within an existing structure, within one block of car-share, or in certain permit-parking areas.
Garage-conversion replacement parking
Local ruleNot required
No replacement parking required for converted garages.
Approval, timeline & cost
Approval path
CA state lawMinisterial (by right)
No public hearing or discretionary design review for a qualifying ADU.
Approval timeline
CA state law60 days
The agency must act within 60 days of a complete application — and the ADU is deemed approved if it does not.
Owner-occupancy
CA state lawOnly for a JADU
No owner-occupancy requirement for ADUs (the prior sunset was removed). A JADU may require owner-occupancy, principally where it shares sanitation with the main house.
Impact-fee waiver
CA state lawWaived under 750 sq ft
An ADU of 750 sq ft or less pays no impact fees (the 750 sq ft threshold itself is exempt under § 66311.5); larger ADUs pay fees proportional to the primary dwelling. JADUs (≤ 500 sq ft) are exempt.
Permits required
Local ruleBuilding permit, Planning permit (unless exempt under state law)
Planning permit required unless state exemption applies.
San Marino-specific factors that can change the answer
State law sets the floor, but these local conditions often decide whether a specific parcel works.
Fire lane and fire flow requirements
New ADUs/JADUs must be on a lot with a 10 ft wide fire lane within 150 ft and 1,000 gpm fire flow if required by the Building Official, unless exempt under state law.
Historic resource restrictions
No ADU may alter the street-facing façade of a historic resource; exterior changes must match original details. Mills Act properties must comply with contract.
San Marino allows up to three units (detached ADU, JADU, and conversion ADU) on single-family lots if site conditions permit, and requires a 6-foot separation between detached ADUs and the primary dwelling. Fire lane and historic property restrictions may apply.
Frequently asked questions
Can I build an ADU in San Marino?
Yes. California's statewide ADU law requires San Marino to approve a qualifying accessory dwelling unit ministerial (by right), plus a junior ADU (JADU) on a single-family lot.
How big can an ADU be in San Marino?
A detached ADU of at least 1,200 sq ft must be allowed, and an ADU of 800 sq ft can never be zoned out by floor-area or lot-coverage limits. A JADU can be up to 500 sq ft.
What are the setback requirements for an ADU in San Marino?
Side and rear setbacks are limited to 4 ft. No front setback may block the mandatory 800 sq ft / 16-ft / 4-ft-setback ADU; otherwise per base zone.
Is parking required for an ADU in San Marino?
Up to 1 space. No parking can be required within ½ mile of transit, for conversions, or for units inside the primary home. When a garage is converted, replacement parking is not required.
How long does ADU approval take in San Marino?
A complete application must be acted on within 60 days, with ministerial (by right) — no public hearing or discretionary design review for a qualifying ADU.
Do I have to live on the property to build an ADU in San Marino?
Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.
Sources
- San Marino Municipal Code § 23.02.25 (Accessory Dwelling Units and Junior Accessory Dwelling Units)
- San Marino Municipal Code § 23.02.25(E)(1)
- San Marino Municipal Code § 23.02.25(H)(3)
- San Marino Municipal Code § 23.02.25(H)(2)
- San Marino Municipal Code § 23.01.01 (Definitions: DETACHED ADU)
- San Marino Municipal Code § 23.02.25(H)(16)
- San Marino Municipal Code § 23.02.25(H)(17)
- San Marino Municipal Code § 23.02.25(G)(3)
- San Marino Municipal Code § 23.02.25(E)(2), (H)(20)
- Cal. Gov. Code §§ 66310–66342 (ADU Law)
- HCD 2025 Accessory Dwelling Unit Handbook
- Cal. Gov. Code § 66317 (ministerial approval, 60-day deadline)
- Cal. Gov. Code § 66333 (junior ADUs)
- Cal. Gov. Code § 66321 (size minimums & height)
- Cal. Gov. Code § 66323 (by-right ADU/JADU, 800 sq ft, 4-ft setbacks)
- Cal. Gov. Code § 66322 (ADU parking; § 66334 covers JADU parking)
- Cal. Gov. Code § 66315 (owner-occupancy)
- Cal. Gov. Code § 66311.5 (impact fees: none for an ADU ≤ 750 sq ft or JADU ≤ 500 sq ft)
Last updated 2026-06-25. This is an AI-assisted summary of San Marino's ADU rules, drawn from its published ordinance and California ADU law — general information, not legal advice, and it may be incomplete or out of date. Verify the controlling rule for your specific parcel with San Marino Planning before relying on it.
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