If you are converting a garage to living space in San Diego and want to rent it out, two legal designations apply: the Accessory Dwelling Unit (ADU) and the Junior Accessory Dwelling Unit (JADU). The distinction is not just terminology. The two categories have different size limits, different kitchen requirements, different parking rules, different owner-occupancy rules (which change periodically under state law), and different fee structures.

Picking the right designation before you draw plans can save you $10,000-$30,000 and months of permit back-and-forth.

What is a Junior ADU

A JADU is a unit of up to 500 square feet created entirely within the existing footprint of a single-family dwelling, which California law explicitly includes attached garages. Key characteristics:

Size cap: 500 square feet. You cannot expand the structure to add square footage to a JADU. Everything has to fit within the existing walls.

Kitchen: An efficiency kitchen is required. This means a sink, a cooking appliance (cooktop, hot plate, or built-in range), and a food prep area. A full refrigerator is not required but is common. A full range with oven qualifies.

Bathroom: Not required. A JADU can share a bathroom with the primary dwelling through an interior door, or have its own. Most owners add a bathroom because a unit without one is hard to rent.

Entrance: Must have its own exterior entrance. It can also have a doorway connecting to the main house, which is not allowed in a full ADU.

Parking replacement: Not required. Converting an attached garage to a JADU does not require you to provide replacement parking anywhere on the property.

Rental rules: A JADU can be rented to any tenant. Historically, JADUs required owner-occupancy on the property, but California state law suspended that requirement and the suspension has been extended. Confirm current law at hcd.ca.gov.

Impact fees: JADUs under 500 square feet are generally exempt from impact fees under California law, which can save $3,000-$8,000 compared to a full ADU.

What is a full ADU

A full ADU is a self-contained dwelling unit with its own kitchen, bathroom, and entrance, separate from the primary home. For garage conversions, a full ADU:

No size cap from state law: While local jurisdictions may apply size limits based on lot coverage, state law does not impose a 500 square foot cap on ADUs. A two-car garage of 400-600 square feet can become a full ADU using the entire space.

Full kitchen required: A full kitchen with a range, sink, and refrigerator is standard for a full ADU. This is what separates it from a JADU in terms of tenant quality of life and rental value.

Full bathroom required: A full bathroom (toilet, sink, shower or tub) is required.

Separate entrance required: A full ADU must have its own exterior entrance with no interior door connecting to the main house.

Parking replacement: For attached garages converted to ADUs, California state law generally prohibits local jurisdictions from requiring parking replacement if the property is within one-half mile of public transit. For detached garages in other areas, parking replacement rules may apply. Confirm with your local building department.

Impact fees: ADUs under 750 square feet are exempt from impact fees under state law. Larger units may owe proportional fees.

Which is right for a typical San Diego garage

For a single-car garage (typically 200-280 square feet): A JADU is the only real option. The space does not support a full ADU with a kitchen, bathroom, bedroom area, and living space that a tenant can comfortably inhabit.

For a two-car attached garage (typically 400-600 square feet): Both are possible. A JADU conversion is faster and cheaper because the fee exemptions apply and the project scope is smaller. A full ADU takes the whole space and produces a unit that rents for $200-$500/month more in most San Diego submarkets, because a fully self-contained unit commands a premium over an efficiency unit sharing access with the main house.

For a two-car detached garage: A full ADU is the more common choice, because the detached structure already has complete separation from the main house and the rental premium justifies the extra cost.

The decision often comes down to budget and timeline. A JADU gets to rental income faster and for less money. A full ADU produces more monthly income and more property value at resale.

Cost comparison

JADU garage conversion (single-car garage, no new bathroom): $30,000-$55,000 for a permitted, code-compliant conversion in San Diego with mid-range finishes.

JADU garage conversion (single-car garage, with bathroom): $45,000-$75,000.

Full ADU (two-car garage, full kitchen and bath): $80,000-$140,000 for mid-range finishes. Add $15,000-$35,000 for high-end finishes.

These ranges reflect real San Diego project costs including permits, mechanical upgrades, subfloor work, and insulation. They are starting points, not quotes.

Questions to ask before you choose

Can your existing garage footprint fit a comfortable living unit at 500 square feet or under? If yes, a JADU may be the faster and cheaper path.

Is the garage attached or detached? Attached garages are more naturally suited to JADUs because the shared-structure connection is already there.

How much can you invest and how long can you wait for rental income? The full ADU produces more income but costs more and takes longer. The JADU gets to market faster.

Do you care about the interior connection to the main house? A JADU can have a door between the unit and the main house. A full ADU cannot.

To discuss which option fits your specific garage and property, visit the garage conversion service page or call (858) 925-5546. We connect San Diego homeowners with experienced, insured local contractors who specialize in both ADU and JADU conversions.

Can a JADU and an ADU both be built on the same lot in San Diego?

Yes. California state law allows one ADU and one JADU per single-family lot. A homeowner could convert a detached garage to an ADU and an interior space (like a bonus room) to a JADU, or vice versa, subject to local zoning and lot coverage rules.

Is a junior ADU always cheaper than a full ADU?

Generally yes, for two reasons: the project scope is smaller (no full kitchen required), and JADUs are exempt from impact fees under state law. The exception is when a JADU requires significant plumbing work to add a bathroom, which narrows the cost gap.

Do JADUs require a separate utility meter?

Not under state law. A JADU can share utilities with the main dwelling. Some owners add a submeter to track usage for tenant billing, but a separate utility account is not required.

What size garage do I need for a comfortable ADU in San Diego?

A two-car garage, typically 400-600 square feet, is the practical minimum for a full ADU that includes a kitchen, bathroom, sleeping area, and small living space. A single-car garage works for a JADU or a studio-style unit where you accept a compact layout.

See the full ADU conversion and junior ADU conversion service pages for what each type involves and how to get connected with local crews.