ADU Builder in San Marino, CA: Local Rules, Permits and Costs

What are the ADU size and setback rules in San Marino?

The city's current ADU ordinance is Ordinance No. O-24-1416, adopted November 11, 2024, and HCD reviewed it on March 16, 2026. The findings letter quotes what the ordinance says. A detached ADU may not exceed 1,200 square feet of floor area and may not exceed one story and/or 16 feet in height. A detached ADU may be up to 18 feet in height if it sits within one-half mile of a major transit stop. A detached ADU must be located six feet or more from each dwelling, building and other structure on the property. ADUs are limited to a maximum of two bedrooms on lots smaller than 12,000 square feet and to three bedrooms on lots 12,000 square feet and larger. State law sets the floor underneath those rules. A city must allow an accessory dwelling unit with at least 800 square feet of interior livable space and with four-foot side and rear yard setbacks, and the maximum floor area for a detached accessory dwelling unit is 1,200 square feet under Government Code Section 66314.

How long does an ADU permit take in San Marino?

Government Code Section 66317 sets the backstop. The city must give written notice of whether an application is complete no later than 15 business days after receiving it, must approve or deny a completed application within 60 days, and a completed application the city has not acted on in that window is deemed approved. The clock stops while an applicant asks for a delay. The city's own pages show how a file moves. Plan check submittal needs 2 sets of plans with any applicable calculations, and for additions the County Assessor asks for an additional site plan and floor plans. Construction in San Marino is governed by the 2022 California Building Codes with local amendments in Chapter 25. Over-the-counter VCA plan check review runs Tuesday from 10:00 A.M. to 11:00 A.M. with the sign-in sheet at City Hall from 7:00 A.M., and only the first 5 applicants to sign in get plan check help at that window. Standard building check plan review runs Monday through Thursday from 7:00 A.M. to 4:00 P.M. and Friday from 7:00 A.M. to 10:00 A.M. The city publishes no ADU-specific review-day count, so the 60-day state deadline is the date to plan around.

How much does San Marino charge for an ADU permit?

San Marino does not publish ADU fee amounts online, so the building and planning fees are posted at City Hall and confirmed at the counter. The Planning Division page states that, under Resolution No. R-25-13, certain building and planning fees were adjusted by 3% based on the Consumer Price Index, and that the updated FY 2026-2027 Schedule of Fees for Services takes effect on July 28, 2026 and is available for review at City Hall. The same page states that credit card transactions have carried a 3% processing fee since July 13, 2025. Impact fees are the one fee line the state sets. Government Code Section 66311.5 bars an impact fee on an accessory dwelling unit with 750 square feet of interior livable space or less and on a junior accessory dwelling unit with 500 square feet or less, and any impact fee above 750 square feet must be charged proportionately to the square footage of the primary dwelling.

How much does an ADU cost in San Marino?

L Square publishes six prefab configurations on its Orange County cost page. Model 600 at $180,000 for 600 square feet with 2 bedrooms and 1 bath. Model 800A and Model 800B at $240,000 each for 800 square feet with 2 bedrooms and 2 baths. Model 1000A and Model 1000B at $295,000 each for 1,000 square feet with 3 bedrooms and 2 baths. Model 1200 at $354,000 for 1,200 square feet with 3 bedrooms and 2 baths. Those are factory-built unit prices for the shell and interior. Site work on a San Marino lot is quoted per property, and the trench length for sewer, water and power, the foundation design on a sloped lot, and the driveway work drive the difference between quotes. City fees sit on top of the unit price.

What should I check before building an ADU in San Marino?

Start with the utility letter and the site plan. The city's Accessory Dwelling Unit Review Application asks for a Service Availability Letter for water and sewer disposal, a site plan showing building separation distances and square footages, the setbacks of the ADU from all property lines, floor plans, the location and dimensions of enclosed and unenclosed parking, elevation drawings for a detached unit, and a Tree Removal Permit Application where it applies. The form also asks for the side setback, the rear setback and the height of the proposed unit, and it asks for a JADU owner-occupancy affidavit plus a deed restriction recorded before the final building inspection. San Marino's Building Division counter is open Monday through Thursday 7:00 A.M. to 5:00 P.M. and Friday 7:00 A.M. to 11:00 A.M., and construction work is prohibited on Sundays and on the listed city holidays under Municipal Code Section 25.01.02(D).

Official San Marino ADU sources

• The city's Planning Division page lists the current ADU ordinance as Ordinance No. O-24-1416 and says the Planning Division is available by appointment only. It states that, under Resolution No. R-25-13, certain building and planning fees were adjusted by 3% based on the Consumer Price Index, that the updated FY 2026-2027 Schedule of Fees for Services takes effect on July 28, 2026 and is available for review at City Hall, and that credit card transactions have carried a 3% processing fee since July 13, 2025. Official source
• The city's Accessory Dwelling Unit Review Application requires a site plan with building separation distances and square footages, the setbacks of the ADU from all property lines, parking locations and dimensions, elevation drawings for a detached unit, a Service Availability Letter for water and sewer disposal, and a deed restriction recorded before final inspection. Its table lists a 150 SF minimum, a maximum of 850 SF for a one-bedroom unit and 1,000 SF for a two-bedroom unit, a height of 16 FT, a 4 FT setback for a new structure, and one parking space of at least 20 FT. Official source
• The city's Plan Checks and Building Permits page says a plan check submittal needs 2 sets of plans with any applicable calculations, that for additions the County Assessor's office requires an additional site plan and floor plans, and that construction in San Marino is governed by the 2022 California Building Codes with local amendments in Chapter 25. It also gives over-the-counter VCA plan check review hours of Tuesday from 10:00 A.M. to 11:00 A.M. and standard building check plan review hours of Monday through Thursday 7:00 A.M. to 4:00 P.M. and Friday 7:00 A.M. to 10:00 A.M. Official source
• The city's Building Division page gives standard counter hours of Monday through Thursday 7:00 A.M. to 5:00 P.M. and Friday 7:00 A.M. to 11:00 A.M., states that under Municipal Code Section 25.01.02(D) all construction work and construction activity is prohibited on Sundays and on the listed city holidays, and lists construction hours of Monday through Friday 7:00 A.M. to 6:00 P.M. and Saturday 9:00 A.M. to 4:00 P.M. Official source
• HCD's March 16, 2026 findings letter on the city's ADU ordinance No. O-24-1416, adopted November 11, 2024, finds the ordinance does not comply with state ADU law and says the city must respond by April 15, 2026 with a plan to amend it or adopt a resolution with findings. The letter quotes the ordinance: a detached ADU may not exceed 1,200 square feet of floor area and may not exceed one story and/or 16 feet in height, a detached ADU may be up to 18 feet in height within one-half mile of a major transit stop, and it must sit six feet or more from each dwelling, building and other structure. Official source
• HCD's August 26, 2024 findings letter reviews the city's earlier ADU ordinance No. O-24-1411, adopted March 13, 2024, finds that it does not comply with state ADU and junior accessory dwelling unit law, and states that the city must provide a written response no later than September 25, 2024, with up to 30 days to respond under Government Code Section 66326. Official source
• California Government Code Section 66317 requires a permitting agency to give written notice of whether an accessory dwelling unit application is complete no later than 15 business days after receiving it, to approve or deny a completed application within 60 days, to treat a completed application it has not acted on within that period as approved, and to toll the 60 days while the applicant requests a delay. Official source
• California Government Code Section 66321 bars a local agency from setting a maximum accessory dwelling unit size below 850 square feet of interior livable space, or 1,000 square feet for a unit with more than one bedroom, requires the city to allow an accessory dwelling unit with at least 800 square feet of interior livable space and four-foot side and rear yard setbacks, and sets a height of 16 feet for a detached unit and 18 feet within one-half of one mile walking distance of a major transit stop. Official source
• California Government Code Section 66314 sets the maximum floor area for a detached accessory dwelling unit at 1,200 square feet and for an attached unit at 50 percent of the existing primary dwelling, caps parking for an accessory dwelling unit at one space per unit or per bedroom whichever is less, bars a local agency from requiring the replacement of off-street parking spaces when a garage, carport or covered parking structure is demolished or converted, and says an accessory dwelling unit does not trigger a fire sprinkler requirement in an existing primary dwelling. Official source
• California Government Code Section 66311.5 says a local agency may not impose an impact fee on an accessory dwelling unit with 750 square feet of interior livable space or less, or on a junior accessory dwelling unit with 500 square feet or less, and that impact fees charged for an accessory dwelling unit with more than 750 square feet of interior livable space must be charged proportionately in relation to the square footage of the primary dwelling unit. Official source