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Junior ADUs in Modesto
Turn spare rooms or an attached garage into a private suite of 500 sq ft or less. Small footprint, short timeline. Licensed and insured.
What is a junior ADU?
It is the smallest legal unit: up to 500 sq ft of interior living area inside a single-family house, which can include an attached garage. It has an outside entrance of its own and at least an efficiency kitchen. The bathroom can be private or shared with the house.
Must the owner live on site?
Only when the bathroom is shared. As of October 2026, Government Code §66333(b) requires the owner to occupy either the house or the junior ADU if the two share sanitation. With a separate bathroom, there is no state owner-occupancy rule.
Can I rent it by the night?
No. State law sets a minimum rental term of more than 30 days for junior ADUs and prohibits short-term rental use, as of October 2026.
Can a junior ADU sit alongside other units?
On a single-family lot, yes: alongside a converted ADU and a new detached ADU of up to 800 sq ft. Multifamily properties cannot add junior ADUs. HCD made this point to Modesto in 2023, when it found the city's ordinance allowed them in mixed and multifamily zones.
What fees apply?
At 500 sq ft or less, a junior ADU pays no impact fees, and it is not treated as a new residential use for utility connection charges (Government Code §66311.5). Building permit and plan check fees still apply.
Is 500 sq ft enough?
It depends on the occupant. One adult, a caregiver or a student can live comfortably in a well-planned junior ADU. Couples and families usually want more room, which points to a detached ADU or an attached ADU.
What does a junior ADU cost?
Block Renovation's 2026 Sacramento guide lists junior ADUs at $50,000 to $100,000, as of October 2026. A new private bathroom or a garage needing major repair pushes the price up.
Related
As of October 2026. Sources: HCD ADU Handbook (March 2026); HCD letter to the City of Modesto (November 27, 2023); Government Code §§66311.5, 66323 and 66333; Block Renovation, Sacramento ADU Costs 2026.
Find out if a junior ADU works
Tell us which rooms or which garage you are thinking of. We check the entry, kitchen and bathroom options.