Jefferson County, MO Fence Regulations: Retaining Walls (2026)
Key Facts
- Permit-exempt height
- 6 feet or less, no surcharge
- Engineering safety factor
- 1.5 against sliding and overturning
- Modular block exception
- Follow manufacturer specs up to 6 ft
- Wood walls
- Must be preservative-treated (Chapter 23)
- Governing sections
- § 500.390, IBC §§ 105.2, 1807.2.1
Summary
Retaining walls up to six feet tall, measured from finished grade to the top of the wall excluding any cap, don't need a building permit in Jefferson County unless they support a surcharge. Walls that do require a permit must be engineered for a 1.5 safety factor against overturning and sliding, per the county's amendments to the International Building Code.
Retaining walls that are not over six (6) feet in height measured from the finished grade to the top of the wall, excluding the cap, unless supporting a surcharge. ... Retaining walls requiring permits shall be designed by an engineer to ensure stability against overturning, sliding, excessive foundation pressure and water uplift. Retaining walls shall be designed for a safety factor of 1.5 against lateral sliding and overturning. Exception: Poured concrete and wood crafted retaining walls not exceeding six (6) feet in height shall not require engineering but shall meet all other design requirements. Premanufactured block retaining systems of a modular nature shall follow manufacturer's specifications. Modular retaining wall systems over six (6) feet in height shall require engineered design supervision. Retaining walls of wood construction shall be preservative treated in accordance with Chapter 23 of this Code.
Full Breakdown
390, exempt retaining walls from a building permit only if they are six feet or less in height, measured from finished grade to the top of the wall (not counting any decorative cap), and are not holding back a surcharge load such as a driveway, parking area, or sloped fill above the wall. 5 against lateral sliding and overturning. The amendment carves out its own exception: poured-concrete and wood-framed retaining walls of six feet or less do not need engineering, though they must still meet every other design requirement in the chapter, and premanufactured modular block retaining systems can instead follow the manufacturer's specifications as long as they stay at or below six feet.
Modular systems taller than six feet require engineered design supervision regardless of the manufacturer's standard details. Any retaining wall built of wood must be preservative-treated in accordance with Chapter 23 of the Building Code, the county's wood-protection standard, so that buried and ground-contact members resist decay.
Violations & Fines
Building a retaining wall over six feet, or one holding back a surcharge, without a permit and engineered design is a Building Code violation under Section 500.300, punishable as a misdemeanor with a fine up to one thousand dollars, imprisonment up to one year, or both, and each day the unpermitted wall stands can count as a separate offense. The Code Official can issue a stop-work order and require the wall to be brought into compliance or removed.
Frequently Asked Questions
Do I need a permit for a retaining wall in Jefferson County?
Does my retaining wall need to be engineered?
Can I use a premanufactured modular block wall system?
Sources & Official References
Other rules in Jefferson County
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