California offers three ADU permit paths: a standard ADU, a Junior ADU (JADU), and a garage conversion. Your budget, timeline, and available space determine which path fits best. A JADU tops out at 500 square feet and sits within your home’s existing walls. A standard ADU can reach 1,200 square feet, whether detached or converted. A garage conversion has no size cap because it reuses a structure you already own. These same rules apply whether you’re building an ADU in Rancho Cucamonga or elsewhere in the San Gabriel Valley.
Junior ADU (JADU)
A JADU sits within the walls of your main home, up to 500 square feet. It typically shares a bathroom with the primary residence and includes its own kitchenette. Because it’s built inside the existing structure, JADUs are usually the fastest and least expensive permit path.
Standard ADU
California law sets a floor on standard ADU size. Cities cannot cap them below 850 square feet for a studio or one-bedroom, or below 1,000 square feet for larger units. Detached ADUs are commonly limited to around 1,200 square feet, though some cities allow more. A standard ADU has its own full kitchen and bathroom and can be attached to, or fully detached from, the main house.
Garage Conversion
Converting an existing garage into a habitable ADU has no size cap under state law since you’re reusing an existing structure. Garage conversions also skip most setback requirements. They don’t require replacement parking, since California law exempts garage, carport, and covered parking conversions from parking rules entirely. Every garage conversion still requires a full building permit and must meet current building code.
Can You Build More Than One?
Yes. On a single-family lot, California law (per the CA Department of Housing and Community Development) allows a combination of one conversion ADU (from existing space), one JADU within the main home, and one detached ADU (up to 800 square feet with 4-foot side and rear setbacks) — all on the same property.
Which Path Is Right for You?
- Choose a JADU if you want the lowest cost and fastest permit, and you’re comfortable sharing a bathroom with the main house.
- Choose a garage conversion if you have an underused garage and want a full, independent unit without new foundation costs.
- Choose a standard detached ADU if you want maximum privacy, a larger footprint, and full design flexibility.
Talk to a San Gabriel Valley ADU Specialist
Every property is different, and the right ADU path depends on your lot, budget, and goals. Contact Potato Construction or call (626) 777-6666 for a free consultation, or explore our ADU services to see examples of our work.
Frequently Asked Questions
A Junior ADU is capped at 500 square feet and must be built within the walls of your existing home.
Yes. Every garage conversion to a habitable ADU requires a full building permit and must meet current building code, even though parking replacement is not required.
Yes. California law allows one conversion ADU, one JADU, and one detached ADU (up to 800 square feet with 4-foot side and rear setbacks) on a single-family lot.
Leave a Reply