Boone County, MO Fence Regulations: Retaining Walls (2026)
Key Facts
- Height trigger
- 4 feet, footing to top
- Engineer required
- Above 4 feet, MO-licensed PE
- Safety factor
- 1.5 sliding/overturning, 3.0 bearing
- Guardrail trigger
- Drop over 30 inches
- Guardrail height
- 36 in. residential, 42 in. commercial
Summary
Boone County requires engineered plans and a building permit for any retaining wall over four feet tall, measured from the footing to the top of the wall; shorter walls need only a basic site plan.
Retaining Wall - Greater than four (4) feet in height. Detailed plans and calculations are required to be submitted to Resource Management Department. However, only the items mentioned above must be submitted prior to the issuance of a building permit. The following additional items must be submitted prior to the beginning of wall construction:
I. A typical section showing wall and footing dimensions, backfill slopes, steel / geotextile reinforcement details, weep hole locations and subsurface drainage systems.
2. Engineering calculations for the design of the waU, noting all assumptions such as concrete and steel reinforcement strengths, soil parameters, surcharges, bearing pressures, safety factors for bearing capacity, overturning, sliding external and internal stability and deep - seated shear failure.
3. Construction plans should specify the type of backfill to be used and any soil testing requirements if not granular. A geotechnical investigation and report is recommended but not required.
Official source re-checked September 7, 2026: the cited page had not changed since it was quoted.
Full Breakdown
Under the county's 2015 building code addendum, retaining walls under four feet in height (measured from the bottom of the footing to the top of the wall) don't need detailed engineering plans, though the county can still require design information for tiered walls. Walls over four feet require a Missouri-licensed professional engineer's sealed plans, calculations, and a post-construction certificate of conformance before Resource Management will approve occupancy. Walls integral to a building's foundation must be approved before a building permit issues. Walls creating a drop of more than 30 inches need a 36-inch (residential) or 42-inch (commercial) fence or guardrail with no more than a 4-inch gap.
Violations & Fines
Starting wall construction without submitting the required plans lets Resource Management issue a stop-work order until the design is reviewed and approved.
Frequently Asked Questions
Does a short retaining wall in Boone County need a permit?
Who has to design a tall retaining wall?
Sources & Official References
Other rules in Boone County
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