California state law has opened the door for most San Marino homeowners to add an Accessory Dwelling Unit (ADU) on their lot. This guide covers the rules, the design choices, and the build process.
State law vs local rules
California Government Code 65852.2 (the state ADU law) sets a floor: every single family lot can have at least one ADU plus one Junior ADU. Cities can add layers on top but cannot block ADUs entirely. San Marino has its own ordinance that further shapes setbacks, height, and lot coverage.
Site feasibility
Before design, walk the lot for setbacks, sewer capacity, electrical service capacity, slope, and easement constraints. Detached new build ADUs need a footprint and yard space. Garage conversions reuse an existing structure. Junior ADUs sit inside the main house. Each path has its own cost basis and construction timeline.
Permits in San Marino
ADU submittals are ministerial in California, meaning the city reviews them administratively without discretionary review. City of San Marino Building and Public Works. typically completes plan check in 60 to 120 days. Design Review Committee reviews exterior work on every project. Front yard fence height limits, mature tree protections, and strict massing rules. Garage conversions usually clear faster than detached new builds.
Construction window
Site clearance, foundation, framing, MEP rough, exterior dry in, interior finish, fixture install, final inspection. ADU builds in San Marino typically run 4 to 7 months of construction. From signed design contract to final inspection most projects total 8 to 14 months.
ADU rules specific to San Marino
State conforming. Design Review Committee involvement on exterior elements.
How Paradigm Builders Can Help in San Marino
Paradigm Builders runs design, permits, and construction across the full residential scope in San Marino. Browse our service pages for what fits your project:
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