ADUs in San Marino: rules, requirements and what fits on your property
What state law allows on any property in San Marino, what the city adds, and what it costs to build. Updated November 6, 2026.
The typical home in San Marino is worth about $2,793,023 (Zillow, September 2026). An ADU adds a second home to that property under the rules below.
State rules now. The city's own rules are being added.
What state law allows in San Marino
These apply in every California city and county. The city can allow more, never less. State rules current to November 6, 2026.
- Detached ADU
Up to 1,200 sq ft. At least 800 sq ft is always allowed.
- Height
16 ft; 18 ft within half a mile of transit, plus 2 ft for a roof that matches the home.
- Setbacks
4 ft from the side and back of the property.
- Parking
None needed within half a mile of transit, or for a conversion.
- Fees
No impact fees up to 750 sq ft. No school fees up to 500 sq ft.
- Timeline
The city must decide within 60 days of a complete application.
What San Marino adds
From the city's zoning code and ADU handbook. These join reports when San Marino is covered.
- Homeowner associations
- HOAs can set reasonable rules but can’t ban ADUs (Civil Code 4751).
San Marino in numbers
Figures from public sources, each with where it was read and when.
- Typical home value
- $2,793,023Zillow Home Value Index, mid-tier, September 2026. Read November 7, 2026.
Questions about ADUs in San Marino
Short answers from the state rules and the city's own figures. Your address gives the answer for your property.
- Can I build an ADU in San Marino?
- Yes. State law requires every California city and county, including San Marino, to allow at least one ADU on a property with a home, and a junior ADU inside the home. Most properties zoned for homes qualify. San Marino can add its own limits but cannot go below the state minimums. Enter your address to see the rules for your property.
- How big can an ADU be in San Marino?
- State law allows a detached ADU of up to 1,200 sq ft, and at least 800 sq ft is always allowed regardless of lot coverage. A junior ADU inside the home can be up to 500 sq ft. An attached ADU can be half the size of the home, and 800 sq ft is always allowed.
- What are the setback and height rules for an ADU in San Marino?
- At least 4 ft from the side and back of the property. Height is 16 ft, or 18 ft within half a mile of major transit, plus 2 ft for a roof that matches the home. San Marino can allow more.
- Do I need parking for an ADU in San Marino?
- No parking is required within half a mile of major transit, for a garage conversion, or when parking is available on the street. When a garage is converted, no replacement parking is required.
- How much does an ADU cost in San Marino?
- Build cost depends on size and the site. ADUCheck's range is $250 to $400 per sq ft for new construction and $100 to $200 per sq ft for a conversion, from the Terner Center ADU owner survey. The typical home in San Marino is worth about $2,793,023 (Zillow, September 2026). City impact fees are waived up to 750 sq ft and school fees up to 500 sq ft.
- Does San Marino have pre-approved ADU plans?
- San Marino has not published its own program that ADUCheck has read. The City of Los Angeles standard plans and the LA County pre-approved plans are the nearest programs; any plan can also be submitted in San Marino as a custom plan.
- How long does an ADU permit take in San Marino?
- State law gives the city 15 business days to say whether your application is complete and 60 days from a complete application to approve or deny it. A missed deadline counts as approval.