Should I turn my attached garage into a JADU or a full ADU?

It depends on the size you need, how you plan to use it, and whether you will live on the property. A JADU is capped at 500 square feet, must be within your single-family home (an attached garage counts), and needs a recorded deed restriction (plus owner occupancy if it shares a bathroom with the house), while a full ADU converted from the same garage has no state size cap and no owner-occupancy requirement. State law lets a single-family lot have one of each, so it is not always either-or.

How the two compare

• Size: a JADU is limited to 500 square feet of interior livable space. An ADU converted from existing space under Government Code section 66323(a)(1) is not subject to unit-size limits.
• Kitchen: a JADU needs at least an efficiency kitchen: a cooking facility with appliances, a food preparation counter, and storage cabinets of reasonable size. An ADU needs a complete kitchen as part of complete independent living facilities.
• Bathroom: a JADU may share a bathroom with your house. An ADU must have its own sanitation facilities.
• Owner-occupancy: since January 1, 2026 (AB 1154), a JADU that shares sanitation with the house requires the owner to live in the house or the JADU; a JADU with its own bathroom does not. ADUs have no owner-occupancy requirement.
• Rentals: a rented JADU must be rented for terms longer than 30 days.
• Deed restriction: a local JADU ordinance must require a recorded deed restriction that bars selling the JADU separately and limits its size and attributes.
• Impact fees: JADUs of 500 square feet or less, and ADUs of 750 square feet or less, are exempt.
• Parking: cannot be required for a JADU, even one converted from an attached garage.

Entrance rules

A JADU created within the house must have exterior access. If it does not have its own bathroom, it also needs an interior entry to the main living area of the house.

Energy Code differences

Converting an unconditioned garage is an addition under the 2025 Energy Code either way. One difference: under Section 150.2(a)1C, a JADU that is an addition to an existing building is exempt from the whole-dwelling ventilation airflow requirement, while a new ADU dwelling unit must meet it. Kitchen and bathroom exhaust apply to both.

What it means for your MEP plans

• JADU: it can usually draw power from your home's panel and share the house's water and sewer. HCD notes that 220-volt circuits are not required for an efficiency kitchen, which can keep electrical changes smaller. Ask early whether your building department will accept the house's existing heating system, since the Mechanical Code limits shared return air between dwelling units.
• Full ADU: expect its own subpanel, a full kitchen circuit layout, a separate bathroom, its own heating and cooling system and thermostat, and whole-dwelling ventilation.
• Either way: decide before the plans are drawn. Switching later changes ventilation, kitchen circuits, plumbing fixtures, and the Title 24 report.

Compare scenarios with the garage conversion guide, building two ADUs on one lot, and sharing plumbing with the main house.

Sources: hcd.ca.gov, energy.ca.gov.