ADU vs JADU in California: the structural, legal, and cost differences

California's current ADU framework is Government Code §§ 66310–66342; JADUs are addressed in Article 3, beginning at § 66333. These provisions were relocated from former §§ 65852.2 and 65852.22. The available combination depends on the statutory pathway, existing dwelling, local implementation and parcel facts, so this comparison is not an eligibility result.

Direct comparison

Maximum size

A JADU is limited to 500 sq ft. For ADUs, Government Code § 66321 prevents a local maximum below 850 sq ft, or 1,000 sq ft for a unit with more than one bedroom, while other statewide safeguards can apply to an 800 sq ft unit. Confirm the local maximum and the proposed pathway rather than treating these floors as one universal size limit.

Location

JADU must be carved out of the existing primary residence (including an attached garage). ADU can be detached, attached, or a conversion.

Kitchen requirements

A JADU uses the efficiency-kitchen standards in Article 3, while an ADU is an independent dwelling with permanent living, sleeping, eating, cooking and sanitation provisions. Existing conditions and the proposed work—not this distinction alone—determine project scope.

Bathroom

JADU can share a bathroom with the primary house. ADU must have its own.

Owner-occupancy

Under § 66333(b), a JADU with shared sanitation requires owner occupancy in the primary dwelling or JADU unless the owner is an exempt governmental agency, land trust or housing organization. A JADU with independent sanitation does not trigger that requirement. Ordinary ADUs generally have no local occupancy requirement, except the qualified-buyer sale condition in § 66341(c)(3). See the owner-occupancy guide.

Permit fees

Under § 66311.5, a JADU with 500 sq ft or less and an ADU with 750 sq ft or less of interior livable space are exempt from the specified impact fees; above that ADU threshold impact fees are proportional to the primary dwelling's square footage. Other permit and connection charges must be reviewed separately.

Cost in real numbers

Existing-space paths may avoid some new-envelope work, but reuse is an assumption until permit history, structure, moisture, energy, fire separation and utilities are investigated. Compare documented scopes in detached vs attached vs conversion and classify known, allowance, excluded and unknown costs in the budget workflow.

Rental income vs cost

Neither unit type establishes rent, demand or return. Compare current, genuinely comparable local listings and documented project scope; HUD Fair Market Rents are area-wide references, not ADU- or JADU-specific predictions. See the rental evidence guide for the limits of that comparison.

Short-term rental

A JADU may not be used as a short-term rental under § 66333(g). Do not infer short-term-rental permission for an ADU from building approval either: check applicable deed restrictions and current local rules in the California short-term rental guide.

Which one is right for you

• —Investigate a JADU when qualifying space exists within a single-family residence and its size, kitchen, sanitation, entrance, occupancy and deed-restriction rules fit the plan.
• —Investigate a conversion ADU when an enclosure exists, then verify permit history and what can actually be retained.
• —Investigate attached and detached ADUs by comparing documented footprints, structural scope, access, utilities, objective standards and mapped constraints—not promised yield or resale outcomes.