Garage Conversion to an ADU in California: Rules & Fees

State law names garages as a place an ADU can go: an ADU can be within the home, “including attached garages,” or detached from it, “including detached garages” (Gov. Code §66314). This guide covers what’s different about a conversion. For the general ADU rules, see ADUs on the Central Coast.

ADU or JADU?

Attached garage: it can become an ADU or a junior ADU (JADU). For a JADU, “enclosed uses within the residence, such as attached garages, are considered a part of the proposed or existing single-family residence” (Gov. Code §66333). A JADU is “no more than 500 square feet of interior livable space” (Gov. Code §66313).
Detached garage: it can become an ADU, but not a JADU. “JADUs are not allowed in accessory structures” (HCD Handbook).

Parking

The garage spaces don’t have to be replaced. When a garage or carport is “converted to an accessory dwelling unit, the local agency shall not require that those offstreet parking spaces be replaced” (Gov. Code §66314).
No parking can be required for the ADU itself either, when it’s “part of the proposed or existing primary residence or an accessory structure” (Gov. Code §66322).

Setbacks, size and height

Setbacks: “No setback shall be required” for an existing structure converted to an ADU, or one rebuilt “in the same location and to the same dimensions” (Gov. Code §66314).
Adding space: a conversion “may include an expansion of not more than 150 square feet” beyond the existing structure, and that expansion “shall be limited to accommodating ingress and egress.” The space must have exterior access (Gov. Code §66323). The Handbook says this 150 square feet applies only to ADUs made from existing accessory structures, not to JADUs.
Size: converting an existing accessory structure or part of the house “is not subject to unit size requirements,” and a conversion’s height is limited to “the dimension of the original structure” (HCD Handbook).

Building onto the garage, or on top of it, is different: the Handbook treats that as a new attached ADU, which has its own size and setback rules.

Building code and fire sprinklers

The conversion still has to be built as a home. “ADU conversions are subject to all applicable building, health and safety, and fire standards for dwellings” (HCD Handbook). State law also lets a local agency change the occupancy code of a space “that was uninhabitable space or was only permitted for nonresidential use,” which describes a garage (Gov. Code §66314). Your building department will say what the space needs.
Fire sprinklers: “The installation of fire sprinklers shall not be required in an accessory dwelling unit or a junior accessory dwelling unit if sprinklers are not required for the primary residence” (Gov. Code §66323).
Existing nonconforming conditions: for these conversions, a local agency can’t require “the correction of nonconforming zoning conditions” as a condition of approval (Gov. Code §66323).

Permit timing

A conversion like this is approved ministerially, without a hearing. The agency has 15 business days to say whether the application is complete, then 60 days to approve or deny a complete application when there’s already a home on the lot. “If the local agency has not approved or denied the completed application within 60 days, the application shall be deemed approved” (Gov. Code §66317).

Replacing a detached garage with a new ADU instead? The demolition permit has to be reviewed with the ADU application “and issued at the same time” (Gov. Code §66314).

Fees and utilities

Impact fees: none for an ADU of 750 square feet or less, or a JADU of 500 square feet or less. Above 750 square feet, impact fees are “charged proportionately in relation to the square footage of the primary dwelling unit” (Gov. Code §66311.5).
Utility connections: for a conversion within existing space, the agency or water company “shall not require the applicant to install a new or separate utility connection directly between the unit and the utility or impose a related connection fee or capacity charge,” unless the unit was built with a new single-family home or is later sold separately (Gov. Code §66311.5).
Plan check and permit fees are separate and vary by city and county.

Renting and property tax

Renting: a unit created this way can be rented, but the rental must “be for a term longer than 30 days” (Gov. Code §66323).
Property tax: the Board of Equalization lists “Conversion of a garage, unfinished basement, or attic into a living area” as new construction, which “is generally assessable and may increase the taxable value of a property” (BOE). Ask your county assessor what it means for your home.

Local planning pages

Cities and counties can be less strict than the state, and their own rules fill in the details:

Santa Barbara County: Accessory Dwelling Units
San Luis Obispo County: Accessory Dwelling Units
City of Santa Barbara: ADU project guidance
In Santa Maria, the City of San Luis Obispo and other cities, check with that city’s planning or building department.

What affects the cost

A conversion reuses walls, a roof and a slab that are already there, but it still has to become a home: typical cost factors include the condition of the existing structure, insulation and windows, how far plumbing and electrical have to run, and the kitchen and bathroom finishes. Our ADU page walks through the steps.

Converting a garage to an ADU: what California law says