Attached ADU Builder for Santa Monica Homes

When an Attached ADU Fits a Santa Monica House

An attached unit makes sense when the backyard is shallow, when the garage sits in the wrong place, or when you want to keep the rear garden whole. It grows out from the house instead of standing apart, usually at the back or along one side. Because it shares a wall, it can often tie into the home's existing sewer line and electrical service with short connections.

We see the option come up most in Wilshire Montana and Sunset Park. In Wilshire Montana, a Craftsman bungalow with a deep lot can take a rear addition that reads as part of the original house. In Sunset Park, the small one-story homes built in the 1940s sometimes have more yard to the side than behind, and an attached unit can use that strip.

Height, Size and Setbacks for Attached ADUs

For height, state law lets an attached unit reach 25 feet unless the zone's own cap is lower, and no city has to allow a third story. Unit size is a local call, but a local cap cannot dip below 850 square feet, or 1,000 for a design with a second bedroom. Santa Monica's own ADU guide sets the specific limits, and we confirm the current numbers before design starts.

Side and rear setbacks of four feet apply here too. For an attached unit, the trickier question is often how the addition affects the main house: whether it blocks windows that light existing bedrooms, whether it changes the path to the backyard, and whether the shared wall needs a fire-rated assembly between the two dwellings.

• Shared wall built as a rated separation
• Separate exterior entrance for the ADU
• Its own kitchen and full bathroom
• Sound control between units
• Height capped by state law and zone

Building Next to a Lived-In House

Attached work touches the house you are living in, so the sequence matters. We open the connecting wall late in the job and close it with the rated assembly the code requires, rather than leaving a gap for weeks. Dust walls and a clear work entrance keep the crew out of your kitchen and hallway.

Older Santa Monica houses often surprise us when the wall comes open. Knob-and-tube wiring, cast iron drain lines and framing that was altered in past remodels show up regularly in pre-war homes. We plan a contingency for this in the schedule and talk through what we find before fixing anything outside the ADU scope.

Attached ADU Cost Factors in Santa Monica

An attached unit saves money on trenching because the utilities are close at hand. It can cost more where the new roof has to meet an old one, or where the main house needs structural work to carry the connection. The foundation must tie into the existing one, and a raised-floor house built on piers needs a different approach than a slab home.

If the addition is 750 square feet or smaller, state law bars impact fees. Plan check and building permit fees still apply. Finishes, window area and whether the unit has one or two bedrooms make up most of the rest of the budget.