Modesto, CA Accessory Structures: Garage Conversions (2026)
Garage conversion rules in Modesto, CA, sometimes called garage-to-ADU or accessory living unit conversions, govern permits, ceiling height, egress, and parking replacement.
Key Facts
- Expansion allowed
- 150 sq ft maximum, solely for ingress and egress
- Nonconforming setback expansion
- 4 ft interior side and 4 ft rear yard minimum
- Replacement parking
- Lost garage parking is not required to be replaced
- City review deadline
- 60 days from completed application, then deemed approved
- JADU size cap
- 500 sq ft, garage conversions count as inside the home
- Minimum rental term
- 30 days or more
- Lot coverage exemption
- ADUs of 800 sq ft or less
Summary
Modesto allows an existing attached garage, or an existing detached garage or other accessory structure, to be converted into an accessory dwelling unit under MC 10-4.504(c). A detached conversion can be enlarged by up to 150 square feet, solely for ingress and egress, and the parking the garage held does not have to be replaced.
Converted . An ADU may be located within a proposed or existing single-family dwelling (e.g., an existing attached garage), or other living space to be converted to an ADU (e.g., master bedroom suite); or an existing detached accessory structure to be converted to an ADU. ... When an existing detached accessory structure is converted to an ADU, a maximum one-hundred-fifty (150) square-foot expansion beyond the dimensions of the existing accessory structure is allowed, provided the expansion is used solely for accommodating ingress and egress. ... Any expansion to an existing structure that is nonconforming as to its setbacks, shall provide a minimum four (4) foot interior side yard and four (4) foot rear yard setbacks. ... When a garage, carport, or other covered parking structure is demolished in conjunction with the construction of an accessory dwelling unit or is converted to an accessory dwelling unit, the lost off-street parking is not required to be replaced.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 71).
Full Breakdown
Modesto treats a garage conversion as one of three ADU types. Section 10-4.504(c) defines a converted ADU as one placed within a proposed or existing single-family dwelling, with an existing attached garage as the named example, or within an existing detached accessory structure. Section 10-4.505(a)(3) repeats the detached-garage case for lots with a single-family dwelling or duplex: the side and rear setbacks of the structure being converted must be sufficient for fire and safety, and a converted ADU inside the dwelling itself must have exterior access.
Size and expansion. Section 10-4.506(c)(1) allows a maximum 150 square-foot expansion beyond the dimensions of the existing detached accessory structure, but only when the added space is used solely for ingress and egress. Where the existing structure is nonconforming as to its setbacks, section 10-4.506(c)(2) requires any expansion to provide a minimum 4 foot interior side yard and 4 foot rear yard setback. Under section 10-4.503(k), an ADU of 800 square feet or less is exempt from the lot coverage figures in Table 4.1-1.
Parking. Section 10-4.508(b) says that when a garage, carport, or other covered parking structure is converted to an ADU, the lost off-street parking is not required to be replaced. The ADU itself needs no more than 1 off-street space under 10-4.508(a), which can be tandem in an existing driveway, and 10-4.508(c)(3) waives the space entirely when the ADU is part of the primary residence or an accessory structure.
Permit process. Section 10-4.503(a) requires ministerial approval of the building permit. On a lot with an existing dwelling the City must approve or deny a completed application within 60 days, and silence past 60 days means the application is deemed approved. A demolition permit for a detached garage that an ADU will replace is reviewed with the ADU application and issued at the same time, and no written notice or placard is required unless the property sits in an architecturally and historically significant district or on a historic register. An ADU does not need fire sprinklers if the primary residence does not.
Junior ADUs. Section 10-4.509(a)(1) counts the conversion of an attached garage as space contained within a single-family residence, so a garage can become a JADU of no more than 500 square feet with a separate entrance and an efficiency kitchen. Under 10-4.502(c), ADUs and JADUs can be rented only in increments of 30 days or more.
Violations & Fines
Sections 10-4.504, 10-4.506 and 10-4.508 print no fine or penalty amount of their own. The enforceable gates are procedural: the conversion needs an approved building permit under 10-4.503(a), and a JADU cannot reach final inspection until the owner records the notice of condition and the deed restriction that 10-4.509(f) and (g) require. A converted ADU also cannot be sold or conveyed separate from the primary residence under 10-4.502(g)(5), and a JADU cannot be sold separately under 10-4.509(h).
Frequently Asked Questions
Can I turn my Modesto attached garage into an ADU?
Do I have to build a new garage or parking space to replace it?
Can I make a detached garage bigger when I convert it?
How long does Modesto have to decide on the permit?
Can I convert my garage into a junior ADU instead?
Sources & Official References
Other rules in Modesto
California rules heatmap·Compare Modesto to another location·View the California accessory structures overview
See something wrong?
Help us keep this page accurate. If you notice an error or outdated information, let us know.