Junior ADU (JADU)

A junior accessory dwelling unit (JADU) is a compact dwelling unit created within the existing walls of a single-family home — often a converted bedroom. Unlike a full ADU, a JADU is carved out of space that already exists rather than added as new floor area, which is why it is generally the least expensive way to add a unit. In many jurisdictions a JADU is capped at a small size (commonly up to 500 square feet) and is built inside the home's existing footprint.

JADUs have a few defining characteristics. They require an efficiency kitchen but may, in some places, share a bathroom with the primary residence. Owner-occupancy of either the main house or the JADU is often required, and the unit usually needs its own exterior entrance. Because a JADU reuses existing space rather than adding floor area, it is a low-cost path to a rentable or multigenerational unit — popular for housing family members, an adult child, or generating modest rental income without building a new structure.

The precise size limits, kitchen requirements, owner-occupancy rules, and whether a separate bathroom is required all vary by state and city, and they can change. JADUs still require a building permit because they create a new dwelling unit, even though no new structure is built.

For builders and homeowners weighing options, the practical question is usually JADU versus a full ADU — see JADU vs ADU for how the two compare on size, cost, and rules. This entry is a general overview; confirm current requirements with your local jurisdiction before you design.