St. Louis County, MO Fence Regulations: Retaining Walls (2026)

The four triggers are independent, so a wall that fails any single one needs a permit even if it satisfies the other three. Height alone is the simplest test: past 3 feet, permit. The surcharge test drops that bar to 2 feet whenever something is loading the soil the wall holds back, and the ordinance names a driveway or pool as the kind of structure that does it, because a wall carrying a car or a body of water is doing more work than its height suggests.

The property line test is a proportion rather than a fixed setback. Measure the wall's height, measure its distance to the line, and if the distance is less than or equal to the height, a permit is required. A wall standing closer to the line than its own height trips this trigger; the same wall set back farther than its height does not. That proportion is also why a wall built directly on the property line always needs a permit: its distance is zero, which is less than any height it could have.

The fourth test measures the whole assembly from the lowest grade to the top of whatever is mounted on the wall, so a low wall with a tall fence on it can pass 6 feet combined and require a permit even though neither element would on its own. Walls in the public road right of way are handled separately and require a Special Use Permit from Highways and Traffic. Every wall must be kept structurally sound.