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ADU build types in Modesto
Four ways to add a unit, and one team for the plans, the permit and the build. Which one fits depends on the lot you start with.
01Detached ADUNew construction in the yard with full privacy. The free regional plans are all detached designs.Detached ADUs
02Garage conversion ADUReworks an existing garage. Parking need not be replaced and existing setbacks can usually stay.Garage conversions
03Attached ADUJoined to the house on one side, entered from its own door.Attached ADUs
04Junior ADUA 500 sq ft or smaller unit within a single-family home.Junior ADUs
Which build type suits my property?
Let the site lead. An intact garage is frequently the lowest-cost legal unit. A wide rear yard with clear access points toward a detached ADU. A big house with rooms nobody uses may only need a junior ADU.
Then match it to the occupant. Renters tend to pay for privacy and a separate door. A parent who needs help nearby may be happier in an attached unit or a junior ADU.
Can one Modesto lot hold several ADUs?
Yes, in many cases. California's Government Code §66323 allows a single-family lot to have a converted ADU, a detached new-build ADU of up to 800 sq ft and a junior ADU all at once, as of October 2026. Apartment properties use other counts and cannot add junior ADUs.
What limits apply to each type?
- Detached: setbacks of 4 feet at the sides and rear; a 16-foot height in most cases, rising to 18 feet near qualifying transit.
- Garage conversion: the existing footprint plus at most 150 sq ft for getting in and out.
- Attached: a height of 25 feet or the zoning limit, whichever is less.
- Junior: at most 500 sq ft of interior living area, within a single-family home.
More on sizes in how big an ADU can be.
As of October 2026, from the HCD ADU Handbook (March 2026) and Government Code §§66314, 66321 and 66323. Modesto's local standards are in its zoning code; we check them per parcel.
Find out what your lot allows
Share the address and a sentence about the plan. We review zoning, setbacks, utilities and whether a free regional plan fits, then reply with your options.