Home Additions in Castro Valley, CA
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County Review for Additions
Castro Valley review: because Castro Valley is unincorporated, the County applies the Castro Valley General Plan and its Residential Design Standards and Guidelines, which are mandatory inside the Castro Valley Urbanized Area; departing from a standard requires discretionary review or a variance. Larger homes on a given lot size can trigger Site Development Review, and the Castro Valley Municipal Advisory Council, which meets on the second and fourth Mondays, reviews those projects and recommends to the Planning Director.
Addition Work
Hazards and Agencies
Hazards: the Hayward Fault runs through western Castro Valley, with Alquist-Priolo zones requiring a geologic investigation. Landslide risk is highest in the northern and eastern uplands, and development on sites with slopes over 30% must be located outside the steep area. Very High fire hazard areas include wooded slopes near Lake Chabot, Cull Canyon, Crow Canyon and Five Canyons, where wildfire-resistant construction applies.
Other agencies: Castro Valley Sanitary District (21195 Center Street, (510) 537-0757) for sewer, Alameda County Fire for access and water supply (roads at least 20 feet wide and no steeper than 14%), and Castro Valley Unified for school fees on additions over 500 sq ft.
399 Elmhurst Street, Room 141, Hayward, CA 94544 · (510) 670-5480 · pe*******@***wa.org
Permit processing Monday, Tuesday, Thursday and Friday 8:30 a.m. to 4:30 p.m., Wednesday 9 a.m. to 4:30 p.m.; over-the-counter plan check by appointment at (510) 670-5440. Inspections online, at (510) 670-5434, or by email.
Alameda County Planning (CDA): 224 W. Winton Avenue, Room 111, Hayward · (510) 670-5400.
Applications run through the Alameda County Permit Portal.
Castro Valley Home Additions FAQ
Does an addition need Site Development Review?
Larger homes for a given lot size can trigger it.
Who is the CVMAC?
The Castro Valley Municipal Advisory Council, which reviews projects and advises the Planning Director.
Are school fees charged?
Castro Valley Unified charges fees on additions over 500 sq ft.
Do I need a geologic study?
In Alquist-Priolo zones along the Hayward Fault.