Multifamily ADUs on Santa Monica Apartment Lots

How Many ADUs a Santa Monica Apartment Lot Can Add

SB 1211 changed the math for Santa Monica apartment owners in 2025. If a multifamily building already stands on the lot, it can gain freestanding ADUs one for one with its existing apartments, topping out at eight. A fourplex may add four; a duplex, two. Separately, rooms nobody lives in (storage, attics, basements, garages) can be turned into units: no fewer than one, and up to one for every four existing apartments.

Lots where the apartment building is still only proposed get less: two detached ADUs at most. We confirm the exact count for your property against current state and city rules, because the math depends on how the city counts existing units and what space qualifies as non-livable.

• Detached ADUs matched one for one to existing units
• Eight detached units at most
• Storage, attic and garage conversions
• Conversions: minimum one, maximum a quarter of units
• Two detached ADUs if the building is still proposed

Rent Control and Tenants on Multifamily ADU Projects

Many Santa Monica apartment buildings are covered by the city's rent control law, and that shapes how an ADU project is planned. The most direct point of contact is parking. When a carport or garage space that came with a rent-controlled apartment disappears into an ADU, the city directs owners to its Rent Control Department, since the tenant's rent may need adjusting.

Construction also happens around people's homes. Tenants need safe paths to their doors, continued access to laundry and trash areas, and notice before utility shutoffs. We plan staging, work hours and utility tie-ins to keep disruption short, and we recommend owners talk with the Rent Control Department early about any changes to housing services.

Multifamily ADUs in Pico, Mid-City and Wilshire Montana

The Pico neighborhood has a high share of long-term renters and many smaller apartment buildings with carports or detached garages at the rear. Those structures are often the first candidates for conversion. In Mid-City, larger lots with courtyard buildings sometimes have unused space along the back property line where a row of detached units can fit.

Wilshire Montana includes Victorian-era duplexes and older multi-unit buildings mixed among houses. On those lots, a detached ADU behind the duplex or a conversion of a basement storage room can add a unit without touching the historic front facade. If a building is listed on the California Register of Historical Resources, extra standards can apply.

Utilities, Sewer and Fire Access for Apartment Lot ADUs

Adding units to an existing apartment lot puts more demand on the building's sewer lateral, water service and electrical service. An older building may already be close to its limits. We review the existing utilities before design so the budget accounts for any new service or meter work, and so the city's plan check has fewer surprises to flag.

Fire department access is another factor. New units at the back of a deep lot need a clear path for firefighters and may need fire sprinklers depending on the building and the code. Garbage and recycling space also has to fit the larger unit count.

Selling or Financing Multifamily ADUs

State law allows ADUs to be sold separately as condominiums only where a city has adopted a local ordinance, and Santa Monica has one in Municipal Code Section 9.31.026. That opens options for some owners, though apartment lots with existing tenants have their own considerations. Most multifamily owners we talk with keep the units as long-term rentals.

State law keeps impact fees off any unit of 750 square feet or less, which helps keep a multi-unit project's fee side small when units are sized carefully. Larger units pay fees proportional to the main building's size.