ADU rules in Monterey County

Detached ADUs are allowed with an existing or proposed home in every unincorporated zone that allows single-family or multifamily dwellings: inland under Title 21 Sec. 21.64.030, and in the coastal zone under Title 20 Sec. 20.64.030 in the HDR, MDR, LDR, RDR, WSC, CGC, MLC, VSC, CAP and AC districts (the county's 12 cities, including Salinas and Monterey, set their own rules). Inland, the 2020 ordinance bars full-size ADUs in resource-constrained areas (B-8 overlays, the North County Planning Area outside the Castroville Community Plan, the first-home-only parts of the Toro and Greater Salinas planning areas, and Specific Plan areas), where only the state-mandated detached unit of up to 800 sq ft, 16 feet tall with 4-foot side and rear setbacks, is allowed (21.64.030.C.1-C.2.a). In the coastal zone, Ord. 5432 (effective December 19, 2025) removed the old North County ban, the Carmel-area 40-acre minimum and the Big Sur 50-unit cap, but ADUs remain prohibited in the Big Sur Critical Viewshed (20.64.030.E.10). Both codes allow one ADU plus one JADU beside a single-family home, and lots with an existing multifamily building may add up to eight detached ADUs (never more than the existing unit count) under the coastal code and Gov. Code 66323(a)(4), which overrides the inland text's limit of two. Everywhere, a unit served by a private well, septic system or a water system of 2 to 199 connections needs Environmental Health approval and is prohibited if water or sewage disposal is inadequate (21.64.030.E.2; 20.64.030.D.1).

Attached ADUs (additions sharing a wall with the house, which in the coastal zone may not have internal circulation with it, 20.64.030.E.7) and conversions of space inside an existing or proposed home or an existing accessory structure, with up to 150 sq ft added for entry and exit, are allowed under both codes; in the inland resource-constrained areas only the state-mandated conversion inside the house or an accessory structure, with exterior access, is allowed (21.64.030.C.2.b). One JADU of up to 500 sq ft inside a single-family home is allowed ministerially everywhere inland, including where new ADUs are otherwise barred (21.64.030.E.1), and in the listed coastal zones with an efficiency kitchen, a separate entrance and, if it shares a bathroom, an interior entry to the house (20.64.030.F.1, F.6-F.8). Existing multifamily buildings may convert non-livable space such as storage rooms, attics, basements or garages into ADUs for up to 25 percent of the building's units (20.64.030.E.1.b; Gov. Code 66323(a)(3), which controls over the inland text's 25-percent-of-floor-area wording under 21.64.030.D). Units previously permitted as senior citizen or caretaker units count as ADUs, and permitted guesthouses may be converted (21.64.030.C.3-C.4; 20.64.030.C.3-C.4).

Inland, every ADU is capped at 1,200 sq ft and every JADU at 500 sq ft (21.64.030.E.9-E.10; the 21.06.372 definition repeats the 1,200 sq ft limit), and because the ordinance applies the state ADU standards 'as may be amended' (21.64.030.D), an attached ADU is also held to 50 percent of the existing home under Gov. Code 66314(d)(4), never below the 800 sq ft interior-livable-space unit that 66321(b)(3) protects. In the inland resource-constrained areas a new detached ADU may not exceed 800 sq ft and 16 feet, and a converted unit may add only 150 sq ft for entry and exit (21.64.030.C.2). In the coastal zone new attached and detached ADUs, and conversions of accessory structures built after March 25, 2024, are capped at 1,200 sq ft in the Carmel Area, North County and Del Monte Forest land use plan areas and at 1,000 sq ft in the Big Sur Coast area and any B-8 combining district, while a conversion of space inside an existing house may not exceed 50 percent of it (20.64.030.E.4); site coverage and floor-area limits may never block an 800 sq ft unit with 4-foot setbacks (E.6). Detached units may be 16 feet tall beside a single-family home and 18 feet on a multifamily lot, or 18 feet (20 feet with a roof pitch matching the house) within half a mile walking distance of a major transit stop or high-quality transit corridor, taller only with a Coastal Development Permit or, inland, a Zoning Administrator Use Permit; attached units follow the zone's height limit (20.64.030.E.2; 21.64.030.E.5; Gov. Code 66321(b)(4)). The coastal 50 percent cap on in-home conversions goes beyond what Gov. Code 66323(b) allows for state-exempt conversions, a conflict HCD has not raised.

Neither code requires the owner to live on a lot with an ADU, and Gov. Code 66315 bars such a requirement. For JADUs, the coastal code still requires the owner to live in the house or the JADU unless the owner is a government agency, land trust or housing organization (20.64.030.F.10), but since January 1, 2026 Gov. Code 66333(b), as amended by AB 1154, allows owner occupancy only where the JADU shares sanitation facilities with the house, and 66339.5 makes the state JADU article control over conflicting local text; the inland code has no JADU owner clause of its own and applies state JADU law (21.64.030.C.2.b.iv, D). In practice a JADU with its own bathroom carries no owner-occupancy requirement anywhere in the unincorporated county, while one that shares the home's bathroom does. A deed restriction recorded before the building permit bars separate sale of a JADU and fixes its size and attributes (20.64.030.F.9; Gov. Code 66333(c)).

Inland, no parking is required for an ADU or JADU: the Sec. 21.58.040 parking table has listed 'ADU/JADU Not Required' since Ord. 5341 (2020). In the coastal zone no off-street parking is required for an ADU and no replacement parking is required when a garage, carport or other covered parking is converted or removed, except on lots inside the areas mapped in Coastal Implementation Plan Appendix 15, 'ADU Parking Required', where each ADU needs at least one off-street space and all other on-site parking requirements must still be met (20.64.030.E.5; the 20.58.040 table points to both). The Coastal Commission's report describes Appendix 15 as a handful of lots along the seaward edge of the Carmel Point neighborhood, where street parking serves Carmel Beach and Carmel River State Beach, and as the only place in the county with on-site ADU parking; that beach-access rule departs from Gov. Code 66314(d)(11) and 66322 but stands under the Coastal Act savings clause of 66329(a). JADUs never need parking (20.64.030.F.5).

Inland, an ADU or JADU needs only a construction (building) permit approved ministerially: the county applies state ADU law, including the Gov. Code 66317 ministerial 60-day process (21.64.030.D), JADUs are expressly ministerial (E.1), and the county's FAQ says an ADU is generally an allowed use inland, though Design Approval in 'D' overlay districts, tree removal or other factors may apply; only an ADU that exceeds both the zone's height rules and 16 feet needs a Use Permit from the Zoning Administrator (E.5). In the coastal zone an ADU or JADU needs a Coastal Administrative Permit processed under Chapter 20.76 with no required public hearing and a decision within 60 days of a complete application, unless it is attached to or inside an existing single-family house and not somewhere 14 CCR 13250 requires a permit (20.64.030.G.1-G.2); Design Approval by the Chief of Planning applies in 'D' districts and is not appealable (D.3), and other project parts (ESHA, slopes over 30 percent, archaeological sites, extra height) can require a Coastal Development Permit, often with a hearing (G.3). Since October 10, 2025 Gov. Code 66329(c) makes the coastal ADU decision unappealable to the Coastal Commission. Environmental Health water and sewer clearance, and in the Cal-Am area an MPWMD water permit, come before the construction permit issues.

ADUs and JADUs may be rented separately for terms over 30 days: the inland code allows rentals 'for more than thirty (30) days' and bars use as a vacation rental of 30 consecutive days or less (21.64.030.E.4), and the coastal code requires 31 consecutive calendar days or longer (20.64.030.D.2), consistent with Gov. Code 66315, 66323(e) and 66333(g). In the Big Sur coastal planning area the certified Land Use Plan (Policy 5.3.3, amended with the October 10, 2025 LCP amendment) prohibits renting an ADU or any part of one for less than 90 days. Separately, the county's vacation rental license law allows vacation rentals only in single-family dwellings and prohibits them in ADUs and JADUs, and a guesthouse cannot be rented apart from the house (Sec. 7.120.040.U, operative October 14, 2024). ADUs cannot be sold separately from the home except by a qualified nonprofit under Gov. Code 66341 (20.64.030.E.11; the inland flat ban yields under 21.64.030.D), and the county has adopted no Gov. Code 66342 condominium ordinance.