Unincorporated Plumas County ADU rules

Maximum size

A detached ADU may be up to 1,200 sq ft of living area. An attached ADU may be up to 50% of the main home's living area, and no more than 1,200 sq ft; state law (Gov. Code § 66321(b)(2)) allows at least 850 sq ft, or 1,000 sq ft with more than one bedroom. An ADU inside an existing accessory structure may add up to 150 sq ft, for entry and exit only. Conversions of existing space, and new detached ADUs on a lot with a multifamily building, have no size limit.

Source: Plumas County Code Title 9, Chapter 2, Article 45 Accessory Dwelling Units, final text (Exhibit B) of Ordinance 2024-1154, § 9-2.4505(c)(2)-(5), accessed 2026-11-01.

Setbacks

Side and rear setbacks are 4 ft, including for an ADU built above a garage. A front setback cannot prevent an ADU under 800 sq ft. No setback is needed for an existing structure converted, in whole or in part, to an ADU, or for an ADU rebuilt in the same place and size as an existing structure.

Source: Plumas County Code Title 9, Chapter 2, Article 45 Accessory Dwelling Units, final text (Exhibit B) of Ordinance 2024-1154, § 9-2.4505(e), accessed 2026-11-01.

Local ADU rules

The County's ADU and JADU rules are in County Code Title 9, Chapter 2, Article 45 (Sections 9-2.4501 to 9-2.4508), added by Ordinance 2024-1154, adopted May 7, 2024 and in effect 30 days later. The County posts the adopted text as Exhibit B (marked "Final") in the same file as the earlier draft. ADUs and JADUs are allowed in any zone that allows homes. The Building Department acts on a complete permit application within 60 days, without a hearing, and within 30 days for the County's ready-made plans.

Source: Plumas County Ordinance 2024-1154 (adopted May 7, 2024), Sections 1-3; Code §§ 9-2.4502, 9-2.4504(a), (d), accessed 2026-11-01.

ADU types and how many

On a lot with a single-family home: one attached or converted ADU, one new detached ADU, and one JADU. On a lot with a multifamily building: detached ADUs, plus ADUs converted from non-living space up to 25% of the existing units, and at least one. On a lot with homes in a mixed use or recreation development: two detached ADUs and one ADU converted from an existing home's living space. An ADU up to 800 sq ft, 16 ft tall, with 4 ft side and rear setbacks cannot be blocked by lot coverage, floor area, open space or minimum lot size rules.

Source: Plumas County Code Title 9, Chapter 2, Article 45 Accessory Dwelling Units, final text (Exhibit B) of Ordinance 2024-1154, § 9-2.4505(a), (b), (c)(1), accessed 2026-11-01.

Height

An ADU may be up to 35 ft tall.

Source: Plumas County Code Title 9, Chapter 2, Article 45 Accessory Dwelling Units, final text (Exhibit B) of Ordinance 2024-1154, § 9-2.4505(d), accessed 2026-11-01.

Parking

One off-street space per ADU. It may be in a setback or tandem on a driveway. No space is needed within a half mile of public transit, in a historic district, for an ADU inside the existing home or an existing accessory structure, where on-street parking permits are required but not offered to the ADU occupant, within one block of a car share vehicle, or when the ADU is applied for together with a new home on the lot. Parking lost when a garage or carport is converted to an ADU does not have to be replaced.

Source: Plumas County Code Title 9, Chapter 2, Article 45 Accessory Dwelling Units, final text (Exhibit B) of Ordinance 2024-1154, § 9-2.4506, accessed 2026-11-01.

Junior ADUs

One JADU up to 500 sq ft is allowed inside a single-family home (including an attached garage), or inside a home in a mixed use or recreation development; not on multifamily lots or in detached accessory structures. It needs its own outside entrance, an efficiency kitchen and a bathroom, which may be shared with the main home. It can be combined with a detached ADU. It needs fire sprinklers only if the main home has them or work underway would require them. It may not be sold apart from the main home, and is not a new unit for utility connection fees.

Source: Plumas County Code Title 9, Chapter 2, Article 45 Accessory Dwelling Units, final text (Exhibit B) of Ordinance 2024-1154, §§ 9-2.201.5, 9-2.4508(a)-(h), accessed 2026-11-01.

Fees, utilities, sprinklers and rental

ADUs pay no impact fees, and no utility connection fee or capacity charge for an ADU converted inside an existing single-family home. An ADU may have its own meters. Septic and water systems must meet County Code Title 6 (Chapters 6 and 9) with Environmental Health sign-off. Fire sprinklers are needed only if the building code requires them for the main home, and a new ADU does not trigger sprinklers in the existing home. A new detached ADU needs a solar panel system (on either roof or the ground). No public improvements or fixes to existing nonconforming conditions are required. ADUs may be rented for more than 30 days, and may be sold separately only as state law allows.

Source: Plumas County Code Title 9, Chapter 2, Article 45 Accessory Dwelling Units, final text (Exhibit B) of Ordinance 2024-1154, §§ 9-2.4505(f)-(i), 9-2.4507(a)-(d), accessed 2026-11-01.

County ready-made ADU plans

The County offers four ready-made ADU plan sets at no cost: 705 sq ft (1 bedroom), 830 sq ft (1 bedroom), 990 sq ft (2 bedrooms) and 1,200 sq ft (two-story, 3 bedrooms). You still need a site plan for Planning review. The County notes the plan sets were drawn under the earlier building code and it is seeking funds to update them to the 2025 California Building Code.

Source: Plumas County Building Department, ADU ready-made plans, Idea Book and ordinance page, accessed 2026-11-01.