Merced County

The Merced County Department of Community and Economic Development - Planning Division issues ADU permits in unincorporated areas. Practical permitting frictions: Williamson Act compatibility review (the dominant constraint - much of unincorporated Merced County is under agricultural preserve contracts), San Joaquin Valley Air Pollution Control District (SJVAPCD) air-quality requirements (the SJV is a federal nonattainment area for PM2.5 and ozone), Sustainable Groundwater Management Act (SGMA, Water Code Sec. 10720 et seq.) groundwater-basin restrictions affecting well permits in critically-overdrafted subbasins (Merced is in the Merced and Chowchilla SGMA subbasins, both critically overdrafted), CAL FIRE State Responsibility Area along the eastern foothills toward Mariposa County, and dairy/feedlot operational-setback rules that interact with ADU placement near commercial operations.

Process overview: Standard ministerial 60-day review per Sec. 65852.2(b) for compliant ADU applications. Williamson Act parcels require compatibility-review confirmation that the proposed ADU supports (does not displace) the principal agricultural use - the parcel must remain in active agricultural production. SGMA-overdrafted subbasin parcels (essentially all of unincorporated Merced County) require well-permit coordination with the local Groundwater Sustainability Agency (GSA) under the Merced and Chowchilla Subbasin GSPs (Groundwater Sustainability Plans). Eastern foothill parcels in the CAL FIRE SRA require Chapter 7A ignition-resistant construction and CAL FIRE defensible space. Septic/well parcels require Environmental Health review.

Impact fees: SB 13 fee waivers apply to ADUs under 750 sqft (no impact fees). Larger ADUs are charged proportionally to the primary dwelling. School district fees apply to ADUs over 500 sqft per Education Code Sec. 17620 (multiple unified school districts overlap unincorporated Merced County: Merced Union HSD, Le Grand Union HSD, Gustine USD, Dos Palos-Oro Loma JUSD, Atwater ESD, Livingston USD).

The Merced County Assessor's Office maintains parcel-level assessment records for the entire county. ADU additions on unincorporated parcels are captured as improvements via shared permit data with the Planning Division. California Proposition 13 caps base-year valuation increases at 2 percent per year on the existing structure; new improvement value (the ADU) is added as a separate line item assessed at fair market value at completion. Williamson Act parcels under preserve contract benefit from agricultural use-value assessment (Sec. 423 of the Revenue and Taxation Code) which is typically substantially below market value; ADU improvement value is added at market on top of the preserved use-value of the underlying agricultural land.

Assessment policy: ADU improvement value is added on the next regular revaluation cycle following completion, not at permit issuance. Per Prop 13, the ADU's value is taxed at 1 percent of fair market value at completion (plus voter-approved local rates), while the existing structure remains at its base-year value plus 2 percent annual cap. Conversion ADUs (within existing structure) typically generate smaller incremental assessments than new detached ADUs. Williamson Act preserve contracts under Cal. Gov't Code Sec. 51200 confer agricultural use-value assessment on the underlying land; ADUs on Williamson Act parcels are permitted but the parcel's overall use must remain consistent with the agricultural preserve contract or the county may initiate non-renewal.

Merced County overlays of consequence: Williamson Act agricultural preserve coverage on a majority of unincorporated parcels (a defining characteristic of the county); SJVAPCD federal nonattainment area for PM2.5 and ozone; SGMA-overdrafted groundwater subbasins (Merced, Chowchilla) under critically-overdrafted designation; FEMA SFHA along the San Joaquin River, Merced River, Mariposa Creek, and tributary drainages; CAL FIRE State Responsibility Area along the eastern foothills (very high FHSZ in the Sierra foothill toe); the San Luis National Wildlife Refuge Complex (San Luis NWR, Merced NWR, Kesterson NWR) on the western county; the Merced National Wildlife Refuge winter-grounds for sandhill cranes; and UC Merced campus / Merced Vernal Pools and Grassland Reserve (UC Natural Reserve System) on the eastern flank near the Lake Yosemite area.

• Williamson Act / California Land Conservation Act preserve contracts
• San Joaquin Valley Air Pollution Control District - federal nonattainment
• Sustainable Groundwater Management Act - Merced and Chowchilla subbasins (critically overdrafted)
• FEMA SFHA - San Joaquin, Merced, Chowchilla River drainages
• CAL FIRE State Responsibility Area - eastern foothills
• San Luis NWR Complex / Merced NWR (federal wildlife refuges)