Modesto, CA Accessory Structures: Garage Conversions (2026)

Under Modesto Municipal Code section 10-4.504(c)(3), a 'converted ADU may be located within an existing single-family dwelling (i.e., in living space to be converted to an ADU, e.g., a master bedroom suite), or within an existing detached accessory structure (e.g., a detached garage).' Section 10-4.506(c)(1) provides that '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.' Existing nonconforming setbacks may be retained: section 10-4.503(d) bars the city from requiring correction of nonconforming zoning conditions as a condition of ministerial ADU approval. Parking for the ADU is capped at one space (section 10-4.508(a)) and waived where the lot is within one-half mile walking distance of public transit (section 10-4.508(c)). This local framework implements California Government Code section 65852.2, which forbids cities from requiring replacement parking when a garage is converted to an ADU. Conversion of a garage to general (non-ADU) habitable space is a discretionary change of use and must satisfy California Building Code chapters 3 and 12 for habitability, light, ventilation, and egress.