San Mateo County, CA Fence Regulations: Neighbor Fence Rules (2026)

Unincorporated San Mateo County's Zoning Regulations (Chapter 8.332) regulate fence height and placement but do not address who pays for a shared boundary fence. That issue is controlled by California Civil Code Section 841, the 'good neighbor fence law,' which applies statewide. Section 841 provides that adjoining landowners are presumed to share an equal benefit from a fence dividing their properties and, unless they agree otherwise in writing, are presumed equally responsible for the reasonable costs of construction, maintenance, or necessary replacement. A landowner who intends to incur such costs must give 30 days' prior written notice to each affected adjoining landowner. The notice must describe the nature of the problem, the proposed solution, estimated costs, the proposed cost-sharing approach, and a timeline. The equal-responsibility presumption can be overcome by a preponderance of evidence that equal cost-sharing would be unjust, considering factors such as disproportionate burden or hardship. San Mateo County's zoning rules layer on top: regardless of cost arrangements, a boundary fence still cannot exceed the 4-foot front and 6-foot side/rear limits without an approved exception. Disputes over cost or maintenance are civil matters between neighbors, not enforced by the county.