A Junior ADU converts existing space inside your home into a permitted dwelling unit — often for under $50,000. Here's what qualifies, what's required, and whether a JADU is right for your property.
Most homeowners have heard of ADUs — backyard cottages, garage conversions, and detached guesthouses. But fewer know about the Junior ADU, or JADU: a lower-cost, faster-to-permit option that converts existing space inside your primary home into a separate dwelling unit. California law specifically created the JADU category to make smaller-scale ADUs accessible to more homeowners.
What Exactly Is a JADU?
A Junior ADU is a dwelling unit of up to 500 square feet created entirely within the walls of an existing single-family home. It must have its own separate entrance (though it can share an entrance with the main house through a common interior corridor), an efficiency kitchen with a cooking appliance, and a food prep area.
Unlike a full ADU, a JADU does not need its own bathroom — it can share the main home's bathroom. This is the key reason JADUs are so much cheaper: you're often converting a bedroom, den, or bonus room without touching plumbing systems.
JADU vs. ADU: Key Differences
| Feature | JADU | Standard ADU |
|---|---|---|
| Max size | 500 sq ft | Up to 1,200 sq ft |
| Location | Inside existing home | Inside, attached, or detached |
| Bathroom required | No (can share) | Yes |
| Full kitchen required | No (efficiency kitchen OK) | Yes |
| Owner occupancy | Required in CA | Not required (AB 3182) |
| Typical cost | $20,000–$60,000 | $60,000–$300,000+ |
| Permit timeline | 30–60 days | 60–120 days |
What Spaces Can Become a JADU?
- An attached garage (most common) — convert one bay of a two-car garage while keeping the other.
- A large bedroom — add a kitchenette alcove and an exterior door.
- A den or bonus room — typically already has a door, just needs a cooking surface and proper egress.
- A finished basement — California basements are rare but ideal for JADUs when they exist.
- An in-law suite that lacks a full kitchen — upgrading to JADU standards makes it legally rentable.
What Does a JADU Require by California Law?
- 1A separate exterior entrance — can share an interior corridor with the main home.
- 2An efficiency kitchen — must include a cooking appliance (cooktop, range, or microwave), counter space for food prep, and a sink.
- 3Maximum 500 sq ft — the unit cannot exceed this size.
- 4Owner occupancy — unlike full ADUs, California law requires the property owner to live on-site (in either the main home or the JADU). This is a key distinction.
- 5A building permit — JADUs still require a permit, but cities must approve complete applications within 60 days.
JADUs are exempt from impact fees, connection fees, and capacity charges in California — by state law. This alone can save $5,000–$20,000 compared to a standard ADU in many jurisdictions.
Is a JADU Right for You?
A JADU makes sense if you have underutilized space inside your home, you plan to live on the property, you want a lower-cost rental unit or suite for a family member, and you want the fastest path to a permitted dwelling unit.
If you need a fully private, separate unit with its own bathroom, or if you want to rent it without living on-site, a standard ADU is the better fit.
At C Hernandez Construction, we help homeowners in Ceres, Modesto, Turlock, and the Central Valley evaluate both options and build the one that fits their property and goals. Contact us for a free walkthrough and estimate.
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C Hernandez Construction · Lic. #1106454 · Ceres, CA · (209) 241-3765