Detached Backyard ADUs in Santa Monica

What Santa Monica Allows for a Detached ADU

Santa Monica's local ADU standards are more generous than the minimum the state sets. A freestanding unit may be two stories or 24 feet tall. Floor area is capped by bedroom count: 850 square feet covers studios and one-bedrooms, and the ceiling climbs to 1,200 once a second bedroom is drawn. Side and rear setbacks are four feet, the same figure state law uses, which lets a cottage sit close to the back property line and keep the middle of the yard open.

These numbers come from the city's ADU guide, which implements Municipal Code Section 9.31.025. Because the approval is ministerial, a design that meets the standards needs only a building permit. Nobody votes on how it looks. We still check the current version of the guide on every project, since the city updates its handouts when state law changes.

• Up to two stories or 24 feet
• 850 sq ft for studio or one-bedroom units
• 1,200 sq ft with two or more bedrooms
• Four-foot side and rear setbacks
• No on-site parking required

Placing a Backyard Cottage on a Santa Monica Grid Lot

The city's flat grid makes siting simpler than in the hills, but it brings its own puzzle. Many blocks have a rear alley, and the best place for a detached unit is often right against it, with the entry facing the alley and the yard left to the main house. That arrangement also shortens the run to the sewer main when the main is in the alley rather than the street.

On the 50 by 150 foot lots common north of Montana, a two-story, two-bedroom cottage fits behind the house with space to spare. In Mid-City and Sunset Park, parcels are often smaller and the old garage already occupies the back corner. There, the choice is between converting that garage, tearing it down and building new, or keeping it and placing a compact unit elsewhere. We sketch each option before you commit.

Adding a Second Unit on R1 Lots and Selling an ADU

Santa Monica lets a single-unit lot combine one converted ADU, one junior ADU and one detached ADU. Lots in the R1 zone get a further option: one more attached or detached unit, as long as a deed restriction is recorded against the property. For an owner with a large R1 parcel, that can mean two new detached buildings rather than one.

The city also adopted an ordinance, Section 9.31.026, that allows an ADU to be sold as a condominium apart from the main house. Most owners never use it, but it changes how a detached unit should be designed if a future sale is on the table. Separate utility meters, a clear path to the street and a site plan that can be divided cleanly all matter more under that scenario.

Preapproved Plans or a Custom Detached ADU Design

The city runs a Preapproved ADU Program with standard plans that have already been reviewed. Using one can shorten plan check, though the site plan, foundation and utility connections are still specific to your lot. A preapproved plan is valid only within the building code cycle under which it was approved, so a plan from an older cycle may need updating before it can be used.

A custom design costs more in drawing time but lets the unit respond to your lot: windows placed away from the neighbor's bedroom, a stair that keeps the footprint small, a roof line that suits the main house. For many Santa Monica owners, privacy on close lots drives the decision more than budget does.

Detached ADU Costs and Utility Connections

A detached unit needs everything a house needs. Water and sewer lines are trenched from the main house or the alley, and power often comes from a new or upgraded electrical service. In Santa Monica, the city supplies water and handles sewer, while Southern California Edison provides electricity. Long trench runs, a panel that cannot carry another kitchen, or a sewer lateral that has to go under the house all add cost.

Square footage matters for fees as well as construction. State law bars impact fees on ADUs of 750 square feet or less, so a one-bedroom drawn just under that size can save money compared with one slightly over it. Two-story designs add stair area, structural engineering and fire separation details, though they free up yard space on tight lots.