What if my main electrical panel or water heater is in the garage I'm converting?

It has to be solved on the plans, not left where it is. Once the garage becomes a separate dwelling unit, your household still needs ready access to its own breakers and equipment, and the ADU occupant should not depend on another household's equipment inside their unit. Typical solutions are relocating the equipment, enclosing it in a space that opens to the outside, or reworking the service so each unit controls its own panel.

The electrical panel

• Access: the electrical code generally requires each occupant to have ready access to the breakers protecting the conductors that supply their unit. If your house's main breaker ends up inside the ADU, your household loses that access.
• Location limits: panels are not allowed in bathrooms or clothes closets and need clear working space in front of them, so a new bathroom or closet cannot simply wrap around the existing panel.
• Common fixes: enclose the panel in a dedicated space with exterior access; relocate the service and main panel to an exterior wall, which requires utility coordination; or add a new panel for the house elsewhere. The ADU then gets its own subpanel inside the unit.
• Capacity: any rework is the time to confirm the service can carry both units with a load calculation.

The water heater

• If it serves your house, it either stays in a space your household can reach, such as a closet with exterior access, or moves to the house.
• A gas water heater that ends up inside living space faces different location, combustion-air, and venting rules than it did in a garage, and some rooms, such as bedrooms and bathrooms, are restricted locations.
• If the ADU gets a new water heater as part of the addition, the 2025 Energy Code's prescriptive options are a heat pump water heater meeting specific installation criteria or, for additions of 500 square feet or less, an electric water heater with point-of-use distribution.

Laundry, gas, and other garage leftovers

• The house's washer and dryer hookups need a new home or a shared-access arrangement, and a dryer vent must still terminate outdoors.
• Gas piping, water shutoffs, and sewer cleanouts in the garage must remain accessible, or be relocated.
• Garage door opener circuits and other garage loads fed from the house panel are removed or reassigned.
• If house HVAC equipment or ducts are in the garage, they need the same treatment, because the ADU cannot share a forced-air system with your house.

What it means for your MEP plans

Start the plan set with an existing-conditions survey that locates the main panel, meter, water heater, laundry, gas piping, cleanouts, and any HVAC equipment in the garage, then show where each item ends up and which unit it serves. Moving a service or meter involves your utility, so build that lead time into your schedule. Related reading: using existing garage electrical, ADU panel upgrades, and garage conversion MEP plans.

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