San Benito County ADU Requirements (2026)
Setbacks, size limits, required documents, and fees for building an ADU in San Benito County, California — including key differences between unincorporated areas, Hollister, and San Juan Bautista.
Who this guide is for
If you're planning to build an accessory dwelling unit (ADU) in San Benito County — whether in unincorporated county land, the City of Hollister, or the City of San Juan Bautista — this page covers the key requirements you need to know before submitting plans.
San Benito County has three distinct jurisdictions that handle ADU permits, and the rules differ between them. This guide breaks down the differences.
Jurisdiction matters
San Benito County includes two incorporated cities and a large unincorporated area, each with its own planning authority:
| Jurisdiction | Planning authority | Key difference |
|---|---|---|
| Unincorporated San Benito County | County Resource Management Agency | Larger lots, septic/well requirements common |
| City of Hollister | Hollister Development Services | City sewer and water, urban lot standards |
| City of San Juan Bautista | City Planning | Historic district overlay may apply |
Important: Pre-approved ADU plans from the state list are not automatically accepted in Hollister or San Juan Bautista. These cities maintain their own review processes and may impose additional local standards.
Before you begin, confirm which jurisdiction your property falls under. The San Benito County Assessor's parcel maps can help identify whether your lot is in incorporated or unincorporated territory.
Size limits
California state law sets the floor for ADU size allowances. Local jurisdictions can be more permissive but not more restrictive.
| ADU type | Maximum size |
|---|---|
| Detached ADU | Up to 1,200 sq ft (state minimum allowance) |
| Attached ADU | Up to 50% of existing living area, or 1,200 sq ft — whichever is less |
| JADU (Junior ADU) | Up to 500 sq ft, must be within existing structure |
| Garage conversion | Full existing garage area (no size penalty) |
A property with a single-family home may have both one ADU and one JADU.
Setback requirements
| Setback | Requirement |
|---|---|
| Side and rear | 4 ft minimum for new construction (state law) |
| Front | Per underlying zoning (varies by jurisdiction and zone) |
| Conversion of existing structure | No setback required if existing structure is maintained |
| Attached ADU | Must meet setbacks of primary structure |
If an existing garage or accessory structure is within 4 ft of the property line, converting it to an ADU does not require additional setbacks. Only new construction triggers the 4 ft minimum.
Required documents
A complete ADU permit application in San Benito County generally requires:
- Completed application form — from the applicable jurisdiction (county or city)
- Site plan — showing property boundaries, existing structures, proposed ADU location, setbacks, and access
- Floor plan — dimensioned layout including rooms, fixtures, exits, and accessibility features
- Elevations — all sides of the proposed ADU showing height, materials, and finish
- Foundation and structural plans — engineered per CBC/CRC requirements for Seismic Design Category D
- Title 24 energy compliance — CF1R forms or equivalent energy calculations
- CalGreen checklist — mandatory green building measures
- Proof of ownership — deed or title report
- Utility will-serve letters — for new connections (detached ADUs on city sewer/water)
For properties on septic systems (common in unincorporated areas), you will also need a septic system evaluation or percolation test showing the system can handle the additional load.
Fees
California law limits ADU fees:
- No impact fees for ADUs under 750 sq ft
- Proportional impact fees for ADUs 750 sq ft and above (proportional to primary dwelling)
- No school fees for ADUs (per Government Code 65995)
- Connection fees must be proportionate to the ADU's burden on the system
Permit fees vary by jurisdiction. As of 2026, expect:
- Building permit fee: $1,500–$4,000 depending on valuation
- Plan check fee: Typically 65% of building permit fee
- Utility connection fees: $2,000–$8,000 for new sewer/water (if required)
Contact the applicable planning department for a current fee schedule before submitting.
Common reasons ADU plans get sent back
Based on review data from San Benito County permit submissions:
- Missing setback dimensions on site plan
- No Title 24 energy forms included
- Construction type or occupancy classification not stated
- Incomplete structural details (no connection details, missing load path)
- Site plan missing north arrow, scale, or property boundary dimensions
- No fire separation details between ADU and primary dwelling (attached ADUs)
Running a pre-check before you submit catches most of these issues in minutes.
Sources
Frequently asked questions
If you own a single-family or multifamily residential property in San Benito County, state law (AB 2221, SB 897) generally requires the county to allow at least one ADU. You can build a detached ADU, an attached ADU, or convert existing space (garage, basement, accessory structure). A Junior ADU (JADU) up to 500 sq ft within the existing footprint is also permitted.
For ADUs built within an existing structure (conversion or JADU), a separate utility connection is generally not required. For new detached ADUs, the county or city may require a new sewer/water connection. Under state law, connection fees must be proportional to the ADU's impact, and no impact fees can be charged for ADUs under 750 sq ft.
The State of California maintains a list of pre-approved ADU plans. However, these pre-approved plans may not be accepted in all jurisdictions. The cities of Hollister and San Juan Bautista have their own planning departments and may have additional local requirements beyond the state standards. Check with the specific jurisdiction before purchasing pre-approved plans.
Under California law (Government Code Section 65852.2), the local agency must act on a complete ADU permit application within 60 days. Incomplete applications will receive a written request for corrections. Actual timelines depend on plan completeness — a pre-check can flag common issues before you submit.
California law requires that either the primary dwelling or the ADU be owner-occupied (this restriction sunsets January 1, 2025 for some jurisdictions). Short-term rental rules vary by jurisdiction. San Benito County, Hollister, and San Juan Bautista may each have different policies. Check local ordinances before planning to use an ADU for short-term rental.
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