Single-Family Residence Zoning and Site Requirements
Single-family homes are primarily built in R-1 districts on lots of at least 5,000 square feet with a 50-foot median width. Other suitable zones include R-S (5,000 sq ft min) and SD (40,000 sq ft min) districts. In Castro Valley, homes are subject to specific Floor Area Ratio (FAR) limits ranging from 0.5 to 0.1 based on total lot size.
In Alameda County, single-family homes are primarily permitted in R-1 (Single-Family Residence) districts, but they are also subject to specific regulations in Suburban, Mixed-Use, and other residential-density districts. All building sites must be recorded as a lot in the office of the county recorder before obtaining a building permit [§ 17.52.100].
Primary Districts for Single-Family Homes
R-1 (Single-Family Residence) Districts
R-1 districts are specifically established to provide and protect neighborhoods of one-family dwellings [§ 17.08.010].
- Permitted Uses: One one-family dwelling per lot is a permitted principal use [§ 17.08.030].
- Minimum Lot Requirements: Every use must be on a building site with an area of at least 5,000 square feet and a median lot width of at least 50 feet (60 feet for corner lots) [§ 17.08.060].
- Design Standards: Development in San Lorenzo, Ashland, Cherryland, Fairview, and the Castro Valley Urbanized Area must comply with the "Residential Design Standards and Guidelines for the Unincorporated Communities of West Alameda County" [§ 17.08.015].
R-S (Suburban Residence) Districts
- Density: The number of dwelling units cannot exceed one unit for every 5,000 square feet of building site area [§ 17.12.050].
- Site Requirements: Building sites must have a minimum area of 5,000 square feet and a median width of 50 feet (60 feet for corner lots) [§ 17.12.060].
- Review Requirements: If a building site area is five times larger than the area required for one dwelling unit, any dwelling placed on it is subject to site development review [§ 17.12.020].
Other Residential and Mixed-Use Districts
- SD (Suburban Density) Districts: Building sites require a minimum area of 40,000 square feet and frontage on a county road [§ 17.17.060].
- R-3 (Four-Family Residence) Districts: While intended for multi-unit use, single-family homes may be built according to density limitations of one unit per 2,000 square feet of lot area, with a general maximum of four units per lot (though this maximum does not apply in the Castro Valley Urbanized Area) [§ 17.14.040].
- M-U (Mixed-Use) Districts: Building sites require a minimum of 5,000 square feet and a median width of 50 feet [§ 17.13.060].
- H-1 Districts: Every use requires a building site of at least 10,000 square feet and an effective frontage of 70 feet [§ 17.32.050].
Cluster Developments
Cluster developments of single-family residences are permitted exclusively in R-1 districts and R-1 combining districts, provided a cluster permit is issued [§ 17.54.310]. These developments are intended to:
- Encourage efficient land use and the preservation of open areas and natural features [§ 17.54.300].
- Provide variety in residence siting and access facility design [§ 17.54.300].
- Maintain compatibility with the general plan and surrounding area development [§ 17.54.300].
Site Development and Floor Area Ratio (FAR)
In the Castro Valley Urbanized Area, one-family dwellings are subject to specific maximum Floor Area Ratio (FAR) limits based on lot size.
| Lot Size | Maximum FAR | Maximum Square Footage |
|---|---|---|
| At 5,000 s.f. | 0.50 | 2,500 s.f. |
| 5,001–9,999 s.f. | 0.3 FAR for area above 5,000 s.f. + 2,500 s.f. | 3,500 s.f. |
| 10,000–20,000 s.f. | 0.40 or 4,500 s.f. (whichever is less) | 4,500 s.f. |
| 20,000+ s.f. | 0.10 FAR + 2,500 s.f. (max 10,000 s.f.) | 10,000 s.f. |
Note: New construction or additions exceeding these maximums require Site Development Review [§ 17.08.110].
General Restrictions
- Yard Regulations: Every building must be constructed on a site that provides specific yards (front, side, and rear) for the district to ensure light, air, and fire safety. Storage of recreational vehicles, utility trailers, or boats in front or required side yards is prohibited in any R district [§ 17.52.330].
- L Districts: Site development review is required for every new dwelling placed on a lot in an L district [§ 17.26.060].
- SC (Scenic Corridor) Districts: New developments must comply with specific provisions regarding roadway buffers and grading. Grading on slopes of 15% or more is prohibited without a variance [§ 17.30.210].