Grass Valley Accessory Dwelling Unit (ADU) Guide
The City of Grass Valley allows the creation of one Accessory Dwelling Unit (ADU) on residential lots that contain an existing legally created primary dwelling. These units can range from 150-square-foot efficiency units up to 1,200-square-foot multi-bedroom residences, provided they meet specific height and setback requirements. In many cases, the City of Grass Valley waives parking requirements for ADUs if the property is located near public transit or within the local Historical District.
Permitted Locations and Creation Methods
In the City of Grass Valley, ADUs (also referred to as "Carriage Houses" when located above a garage) are permitted in all primary residential zones, including Residential Estate (RE), Single-Family Residential (R-1), Two-Family Residential (R-2), Medium Density Residential (R-2A), and Multiple Dwelling Residential (R-3) [Section 17.22.030]. They are also permitted in Traditional Community Development zones such as Neighborhood Center (NC), Neighborhood General-2 (NG-2), and Neighborhood General-3 (NG-3) [Section 17.21.030].
According to the Grass Valley Development Code, an ADU may be created through four primary methods:
- Internal Conversion: Altering existing space within a dwelling where facilities are not shared.
- Space Conversion: Converting an attic, basement, garage, or other uninhabited portion of the primary structure.
- Addition: Adding new square footage onto an existing residential structure.
- New Construction: Building a completely separate detached structure on the lot [Section 17.44.190.B].
Development Standards
The City of Grass Valley enforces specific physical standards to ensure ADUs remain secondary to the primary residence. Detached ADUs must maintain a minimum separation of 10 feet from the primary dwelling [Section 17.44.190.C.8].
Unit Size and Height Requirements
The maximum size of an ADU in Grass Valley is strictly regulated by the number of bedrooms and its relationship to the primary house.
| Feature | Requirement |
|---|---|
| Minimum Size (Efficiency Unit) | 150 square feet [Section 17.44.190.C.3.a] |
| Maximum Size (1 Bedroom) | 850 square feet [Section 17.44.190.C.3.b] |
| Maximum Size (2+ Bedrooms) | 1,000 square feet [Section 17.44.190.C.3.b] |
| Absolute Maximum Limit | 1,200 square feet or 50% of the primary dwelling's floor area (whichever is less) [Section 17.44.190.C.3.d] |
| Maximum Height (Detached) | 16 feet [Section 17.44.190.C.3.c] |
Setback Requirements
Grass Valley provides relief for ADU setbacks compared to standard residential structures to encourage their development.
| Boundary Type | Setback Requirement |
|---|---|
| New Detached ADU (Side/Rear) | 4 feet [Section 17.44.190.C.9] |
| Conversion of Existing Legal Structure | 0 feet (No setback required if converted in the same location and dimensions) [Section 17.44.190.C.9] |
| Front Yard | Must comply with the underlying zone's front setback [Section 17.44.190.C] |
Parking Requirements
While the standard requirement is one parking space per ADU, the Grass Valley Development Code provides several exemptions where no additional parking is required.
Standard Ratios
- Studio and 1-Bedroom Units: 1 accessible off-street space.
- 2+ Bedroom Units: 2 off-street spaces.
- Tandem Parking: Allowed in Grass Valley for ADU use [Section 17.44.190.C.6].
Exemptions from Parking
No additional parking is required for a Grass Valley ADU if the unit meets any of the following criteria:
- The ADU is located within one-half mile of public transit.
- The property is located within the City of Grass Valley Historical District.
- The ADU is part of an existing primary residence or an existing accessory structure.
- A garage or carport is demolished in conjunction with the construction of the ADU [Section 17.44.190.C.6].
Operating and Legal Restrictions
- Prohibited Housing Types: Mobile homes, recreational vehicles (RVs), and other movable habitable spaces cannot be used as ADUs in the City of Grass Valley [Section 17.44.190.B.4].
- Separate Sale: The Grass Valley Development Code prohibits the separate sale or financing of an ADU through a condominium plan or subdivision. The ADU must remain under the same ownership as the primary residence [Section 17.44.190.E].
- Short-Term Rentals: New ADUs created under these standards may not be used for short-term rentals (rentals of less than 30 days) [Section 17.44.190.C.7.c].
- Junior ADUs (JADUs): Grass Valley also allows JADUs, which are limited to 500 square feet and must be contained entirely within a single-family residence [Section 17.100.020].
Sections Cited
- Section 17.21.030 - Purposes of the traditional community development zones
- Section 17.22.030 - Residential zone allowable land uses and permit requirements
- Section 17.36.040 - Number of parking spaces required
- Section 17.44.190 - Accessory dwelling units (ADU)
- Section 17.100.020 - Definitions of specialized terms and phrases