ADU rules in Nevada County

Detached ADUs are allowed in unincorporated Nevada County on any parcel where residential use is allowed by right or by use permit, regardless of minimum parcel size or zoning density, through zoning compliance (a ministerial site plan review) and a building permit. The use tables list ADUs and JADUs as 'A' (allowed with zoning compliance and a building permit) in the RA, R1, R2, R3, AG, AE, FR, TPZ, IDR, P and REC districts; only Open Space (OS), which allows no dwellings at all, lists them as not permitted. On a single-family lot the Planning Department's 2025 ADU Policy (approved 2-27-2025) allows one new detached or attached ADU of up to 1,200 sq ft beside a conversion ADU and a JADU, which overrides the codified one-ADU-plus-one-JADU limit in 12.03.191.C.3; on a lot with a multifamily dwelling, Ord. 2557 (adopted 9-15-2026, operative 10-16-2026) raises the codified detached count from two to eight. Wildfire items (a site-specific Fire Protection Plan in High and Very High Fire Hazard Severity Zones or beyond the dead-end road limit, fire-safe driveway access) and septic capacity are ministerial building-permit requirements, not approval gates.

Attached additions and conversions of existing space are allowed on the same ministerial basis as detached units: 12.03.191.C.1 names an attached structure, a manufactured home, or a converted area within a legally existing residential unit or accessory structure as qualifying ADU forms. The 2025 ADU Policy lets a conversion ADU created from existing space under state law sit beside a JADU and one new attached or detached ADU on a single-family lot. A JADU must be built within the walls of a proposed or existing single-family residence, with a separate entrance and a cooking facility (12.03.191.C.2). Attached units take the 50 percent size rule described under maxSize.

Section 12.03.191.C.1.a caps an ADU, measured from the interior walls, at 1,200 sq ft when detached and, when attached, at 50 percent of the existing residence's gross floor area but no more than 1,200 sq ft; the 2025 ADU Policy restates the 1,200 sq ft ceiling for the one new attached or detached unit. The percentage rule cannot shrink an attached ADU below the 800 sq ft that Gov. Code 66321(b)(3) guarantees, and the state-exempt detached unit in 12.03.191.C.18 (cited to legacy Gov. Code 65852.2(e)(1)(B), now 66323(a)(2)) is 800 sq ft and 16 ft tall. A conversion ADU inside existing space follows Gov. Code 66323(a)(1) under the 2025 policy rather than the local percentage cap, JADUs are limited to 500 sq ft by the state definition the code adopts, and a tiny home on wheels used as an ADU may not exceed 400 sq ft measured by exterior walls (12.03.310.C.7). Other heights come from the base zoning district.

Section 12.03.191 imposes no owner-occupancy rule on ADUs, and Gov. Code 66315 bars one. The section's JADU clause (C.2.a) still requires the single-family residence containing a JADU to be owner-occupied, in either the main house or the JADU, unless the owner is a governmental agency, land trust or housing organization, and Ord. 2557 re-enacted it unchanged in September 2026. Since 1-1-2026 Gov. Code 66333(b) (as amended by AB 1154 and SB 543) allows a JADU owner-occupancy requirement only where the JADU shares sanitation facilities with the main home, so the universal local clause is overridden for a JADU with its own bathroom. The county FAQ's rule that the ADU applicant must be the current owner is an application requirement, not an occupancy requirement.

The parking table in Section 12.04.109 (labelled Table 12.04.180.b, a recodification leftover) lists 'No additional parking is required' for both accessory dwelling units and junior accessory dwelling units, with no zone, transit or size condition. Its footnote (2)(e) also waives parking where a garage, carport or covered space is converted or demolished in conjunction with an ADU or JADU, and Gov. Code 66314(d)(11) separately bars requiring replacement of those spaces for the main home. The county code has carried this no-parking rule since Ord. 2533 (12-5-2023).

Section 12.03.191.C says an ADU or JADU 'shall be ministerially permitted', subject to zoning compliance and building permit issuance, and Section 12.05.040 makes zoning compliance a Planning Director site plan review filed with the building permit, with no hearing; Gov. Code 66317 adds the 60-day deemed-approved clock. The Fire Protection Plan, septic review, fire-safe driveway items and the recorded deed restriction are submittals inside that ministerial review. The separate 'second dwelling unit consistent with allowed density' in Section 12.03.192 (no size cap, parcels at least twice the minimum lot size) needs an Administrative Development Permit, counts toward density, and is not an ADU.

Section 12.03.191.C.3 lets an ADU or JADU be rented for long-term use only (30 consecutive calendar days or more) and prohibits short-term rentals, and C.6 requires the owner to record a deed restriction carrying that rule before the building permit issues; the county has required it for ADUs built after 4-25-2019, so older ADUs without one may still be rented short term. ADU short-term rentals are allowed only on a working farm or ranch with an agritourism use verified by the Agricultural Commissioner, within the Soda Springs Rural Center, and inside the Truckee sphere of influence, where the Town of Truckee's zoning rental standards apply instead. The county has no short-term rental permit program: hosts register with the Treasurer-Tax Collector and pay the 10 percent transient occupancy tax (Title 5, Chapter 4). ADUs and JADUs may not be sold separately from the main home, and the county has not opted into Gov. Code 66342 condominiums, leaving only the state 66341 nonprofit route. JADUs and state-exempt units must rent for longer than 30 days under Gov. Code 66333(g) and 66323(e), so the county's 30-day floor is one day short for them and its short-term exceptions cannot reach them.