Accessory Dwelling Unit (ADU) Size Standards in Grass Valley

In the City of Grass Valley, the maximum square footage for an Accessory Dwelling Unit (ADU) is generally capped at 850 square feet for a one-bedroom unit and 1,000 square feet for a unit with more than one bedroom. Regardless of bedroom count, the City of Grass Valley Development Code stipulates that an ADU may not exceed 1,200 square feet or 50% of the floor area of the primary dwelling, whichever is less [Section 17.44.190].

Accessory Dwelling Unit Size Classifications

The Grass Valley Development Code establishes size requirements based on the type and configuration of the proposed unit. These standards are intended to allow for various housing types while ensuring the ADU remains incidental to the primary residence in the City of Grass Valley.

Technical Standards for ADU Floor Area

The following table outlines the specific square footage requirements and limitations for Accessory Dwelling Units within the City of Grass Valley:

Unit Type or Constraint	Square Footage Standard
Efficiency Unit	Minimum 150 sq. ft.
One-Bedroom ADU	Maximum 850 sq. ft.
More than One Bedroom ADU	Maximum 1,000 sq. ft.
Detached ADU (Standard)	Up to 800 sq. ft. (with 16 ft. height and 4 ft. setbacks)
Absolute Maximum Cap	1,200 sq. ft.
Primary Dwelling Ratio	May not exceed 50% of primary dwelling floor area

Attached vs. Detached ADU Size Provisions

The City of Grass Valley provides specific flexibility for different construction methods. For detached ADUs, the Grass Valley Development Code permits units up to 800 square feet with a maximum height of sixteen feet, provided they maintain four-foot side and rear yard setbacks [Section 17.44.190].

For attached units or larger detached units that do not fall under the 800-square-foot "safe harbor" provision, the City of Grass Valley applies the stricter of two caps: the 1,200-square-foot absolute limit or the 50% primary dwelling limit [Section 17.44.190].

Impact Fees Based on Size

The City of Grass Valley does not impose any impact fees on the development of an Accessory Dwelling Unit that is less than 700 square feet. If an ADU in the City of Grass Valley is 750 square feet or larger, impact fees are charged proportionately in relation to the square footage of the primary dwelling unit [Section 17.44.190].

Junior Accessory Dwelling Units (JADUs)

The City of Grass Valley also allows for Junior Accessory Dwelling Units. These are distinct from standard ADUs and are limited to a maximum size of five hundred square feet. They must be contained entirely within a single-family residence [Section 17.100.020].

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