Can I convert part of my garage to an ADU and keep the rest for parking?

Yes. State ADU law allows an ADU within the existing space of a garage, and nothing requires you to convert all of it, so a smaller ADU beside a smaller garage is a workable layout. The catch is that you now have a garage sharing a wall, and sometimes a ceiling, with a dwelling unit, so the code's dwelling-garage separation rules apply to the new wall and the ADU's systems have to be planned around that boundary.

The parking question

Keeping parking is your choice, not a city mandate. HCD's ADU Handbook explains that a local agency may not require replacement off-street parking when a garage is converted to an ADU, and ADUs located within an existing structure are exempt from ADU parking standards.

Separating the ADU from the remaining garage

• Wall and ceiling protection. The California Residential Code requires gypsum board on the garage side of the wall between a garage and a dwelling, with heavier Type X protection at the garage ceiling where habitable rooms sit above it.
• Doors. A door between the garage and the ADU must meet the code's garage-to-dwelling door requirements, including a self-closing door of solid or rated construction, and a garage cannot open directly into a sleeping room.
• Ducts. Ducts that run in the garage or pass through the separation must be sheet metal or another approved material, with no openings into the garage.
• Penetrations. Pipes, cables, and boxes in the separating wall must be sealed so the separation stays intact.

Energy and air quality

Under the 2025 Energy Code, converting garage space into a dwelling unit is an addition. The wall between the ADU and the remaining garage separates conditioned from unconditioned space, so it is insulated and modeled that way in the Title 24 report. As a new dwelling unit, the ADU needs whole-dwelling mechanical ventilation based on its own floor area, kitchen and bath exhaust, and ECC-rater verification of items such as the ventilation fan.

An attached garage can also trigger carbon monoxide alarm requirements, so expect CO alarms in the ADU along with smoke alarms.

If you are in a fire hazard zone

The 2025 California Wildland-Urban Interface Code limits gaps around garage vehicle doors and requires battery backup on automatic garage door openers serving a residence, as LADBS's Fire Hazard Severity Zone checklist summarizes. If you keep a working garage door, plan for both.

What it means for your MEP plans

• Electrical: Show which panel feeds the remaining garage lights, receptacles, door opener, and any EV charging. Those loads usually belong to the main house, not the ADU.
• Mechanical: Keep the ADU's ducts and air handler out of the garage, or detail them to meet the separation rules. A ductless system inside the ADU avoids most conflicts.
• Plumbing: Note any water heater, laundry, or gas piping that stays in the garage, and how it is protected and reached.
• Title 24: The report's wall assemblies and conditioned floor area must match the exact line between ADU and garage on your floor plan.

Related reading: the garage conversion guide, what happens to the garage door, and fire separation between the ADU and the main house.

Sources: hcd.ca.gov, energy.ca.gov, energy.ca.gov, dbs.lacity.gov.