What is a JADU, and how is it different from an ADU?

A junior accessory dwelling unit (JADU) is a unit of up to 500 square feet of interior livable space created entirely within a single-family home, including an attached garage. Unlike a regular ADU, it can share a bathroom with the main house, it only needs an efficiency kitchen, it cannot be detached, and it carries a deed restriction against separate sale.

The legal definition

Government Code section 66313(d) defines a JADU as a unit no more than 500 square feet of interior livable space, contained entirely within a single-family residence, that may have its own sanitation facilities or share them with the existing structure. Since January 1, 2026, the size limit is measured as interior livable space, which HCD says includes bedrooms, bathrooms, kitchens, laundry rooms, closets and interior stairs.

Key JADU rules (sections 66333 to 66339)

• One per lot, only on lots zoned for single-family homes with an existing or proposed single-family residence. JADUs are not allowed on multifamily lots or in detached accessory structures.
• Inside the house. It must be built within the walls of the home; attached garages count as part of the home.
• Separate entrance from the home's main entrance. If the JADU has no bathroom of its own, it must also have an interior entry to the main living area.
• Efficiency kitchen with a cooking facility with appliances, plus a food preparation counter and storage cabinets of reasonable size for the unit.
• Deed restriction prohibiting separate sale and limiting the unit's size and attributes.
• Rentals must be for terms longer than 30 days, and owner occupancy is required if the bathroom is shared.
• No parking can be required, and a JADU of 500 square feet or less is exempt from impact fees.

How a JADU compares with an ADU

• An ADU must provide complete independent living facilities, including its own sanitation. A JADU can share a bathroom.
• An ADU can be attached, detached or converted, on single-family or multifamily lots. A JADU must be inside a single-family home.
• ADUs have no owner-occupancy requirement. JADUs that share sanitation do.
• You can have both: state law requires agencies to allow one converted ADU and one JADU on a single-family lot, and HCD says those can be combined with a new detached ADU.

What this means for your MEP plans and permit set

A JADU usually has a smaller MEP scope than a detached ADU, but it still needs a permit and plans showing the efficiency kitchen, any new bathroom, ventilation, required smoke and carbon monoxide alarms, and how its circuits and plumbing tie into the house. Converting an attached garage adds work such as insulation, Title 24 compliance for newly conditioned space and drain routing through the slab. See ADU and JADU combinations, Title 24 for garage conversions, and California ADU requirements. Confirm local JADU rules with your planning department.

Sources: leginfo.legislature.ca.gov, leginfo.legislature.ca.gov, leginfo.legislature.ca.gov, leginfo.legislature.ca.gov, leginfo.legislature.ca.gov.