Solano County, CA Fence Regulations: Retaining Walls (2026)

Solano County Code Section 31-30(q), part of the design standards in the county's Grading, Drainage, Land Leveling, and Erosion Control ordinance, prohibits cutting or filling land within five feet of a property boundary unless the applicant installs a retaining wall. The provision then ties the wall's allowable height directly to its setback from the line: the wall cannot be taller than its own distance from the property boundary, so a wall built two feet from the line is capped at two feet, while one built five feet back can reach five feet. The Director may grant exemptions from this standard, but only with the written approval of both the adjoining landowner and county staff, so a taller or closer wall generally requires the neighbor's sign-off as well as the county's.

Because the rule sits inside Chapter 31 rather than a standalone fence chapter, any retaining wall triggering it is also subject to the grading permit machinery around it. Section 31-22(c) exempts an excavation below finished grade for a retaining wall's footing when it is authorized by a valid building or encroachment permit, but that exemption covers only the footing excavation itself, not the general prohibition on cuts and fills near the boundary line in Section 31-30(q). Retaining walls built as part of a larger grading project must still be reflected in the grading plan required under Section 31-24 or 31-26, which requires elevations, dimensions and the extent of proposed grading, and in the erosion control plan describing land treatment and structural measures under Section 31-24(d). Section 31-42(a) then requires the applicant to install and maintain all approved measures, which for a bordering retaining wall means keeping the structure within its permitted height and location once built.