Butte County, CA Accessory Structures: Garage Conversions (2026)
Garage conversion rules in Butte County, CA, sometimes called garage-to-ADU or accessory living unit conversions, govern permits, ceiling height, egress, and parking replacement.
Key Facts
- Code Section
- Butte County Code section 24-172(H)(1)(a) and 24-172(H)(3)(c)
- Setback for existing-structure conversion
- Zero (none required)
- Replacement parking
- Not required when converting a garage, carport, or covered parking to an ADU
- Expansion limit
- Up to 150 sq ft expansion of existing structure, with 4-foot side/rear setback
- Permit type
- Ministerial (no hearing or discretionary review)
- Short-term rentals
- Prohibited (30 days or less)
Summary
Butte County allows conversion of an existing garage or accessory structure into an ADU with no required setback and no replacement parking, provided the parcel is within a water and sewer service area and the conversion meets building code.
H. Development Standards. 1. Setbacks. The following setbacks are applicable for all accessory dwelling units: a. An existing structure may be converted into an accessory dwelling unit or junior accessory dwelling unit without a setback. If the existing structure requires an expansion of 150 square feet or less to accommodate an accessory dwelling unit or junior accessory dwelling unit, the setback shall be no less than 4 feet from side and rear property lines, or as otherwise required to provide for fire safety. b. If the parcel cannot accommodate the setback imposed by the applicable zone, the setback maybe no less than 4 feet from side and rear property lines for new accessory dwelling units not developed within or converted from an existing structure. 3. Parking. The following parking standards are applicable for all accessory dwelling units: a. A maximum of 1 space shall be provided per bedroom or per accessory dwelling unit, whichever is less. b. Tandem parking (i.e., when two or more vehicles are parked on a driveway or in any other location on a lot, lined up behind one another) within an existing driveway, and within setbacks is allowed unless specific site conditions and topography make tandem parking infeasible. c. No replacement parking is required for the conversion of an existing parking area such as a garage, carport or covered parking structure into an accessory dwelling unit. d. No parking shall be required for accessory dwelling units if any one of the following applies: 1. The accessory dwelling unit is within one-half mile walking distance of public transit, including transit stops. 2. The accessory dwelling unit is located on a site of historic significance. 3. The accessory dwelling unit is part of the proposed or existing primary residence or an accessory structure.
Full Breakdown
Under Butte County Code section 24-172(H)(1)(a), an existing structure (including a garage, carport, or covered parking structure) may be converted into an accessory dwelling unit or junior accessory dwelling unit without any setback. If the conversion requires an expansion of 150 square feet or less to accommodate the ADU or JADU, the expanded portion must be no less than 4 feet from side and rear property lines (or whatever fire-safety setback applies). Critically, section 24-172(H)(3)(c) provides that 'no replacement parking is required for the conversion of an existing parking area such as a garage, carport or covered parking structure into an accessory dwelling unit' - meaning homeowners do not have to build a new garage or covered parking spot to replace one they convert.
Junior ADUs created by converting space within a single-family dwelling may include separate sanitation facilities or share the main house's bathroom. Conversions are subject to the same ministerial approval as new-construction ADUs, must comply with the state-mandated short-term rental prohibition (no rentals of 30 days or less), and a deed restriction must be recorded before the permit issues. Garage conversions in unincorporated Butte County are limited to parcels within a water and sewer service provider's boundaries - a significant constraint given the predominantly rural, well-and-septic-served character of the county.
Violations & Fines
Converting a garage to a separate dwelling unit without a permit, deed restriction, or in an area outside a water/sewer service boundary can result in a stop-work order, mandatory restoration of the structure to its original use, and short-term rental violations carry the same enforcement as the underlying ADU ordinance.
Frequently Asked Questions
Do I have to build a new garage if I convert my existing garage into an ADU?
Does my converted garage have to meet the normal side-yard setback?
Can I convert a detached garage in a rural area of Butte County?
Sources & Official References
Other rules in Butte County
California rules heatmap·Compare Butte County to another location·View the California accessory structures overview
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