Retaining Walls in St. Louis

A retaining wall is a structural and drainage project, not simply stacked landscape material. The right scope depends on wall height, soil, slope, nearby loads, property lines, water movement, access, appearance, and the rules for the exact address.

Start with the wall’s job

Some low landscape walls shape a garden bed. Others support a driveway, patio, pool, building, steep slope, fence, or neighboring grade. Those are materially different projects. Document the retained height, total length, changes in elevation, nearby improvements, signs of movement, and where surface water travels during rain before requesting bids.

Common wall systems

• Segmental concrete block: modular units may be used with compacted aggregate, drainage material, and geogrid where the design requires reinforcement.
• Poured concrete: formed walls can provide a clean structural solution but depend on engineered reinforcement, footing design, joints, waterproofing or drainage details, and site access.
• Masonry or stone: appearance varies widely, and the structural backup, footing, drainage, and workmanship matter more than the visible face alone.
• Timber: may fit some smaller projects, but decay, fasteners, drainage, and expected service life should be addressed in writing.

No single system is automatically best. A qualified designer or contractor should connect the proposed system to the site’s loads, soil, drainage, geometry, and intended lifespan.

What drives retaining-wall cost?

Useful bids separate demolition and disposal, excavation, access, temporary support, footing or leveling pad, drainage aggregate and pipe, reinforcement or geogrid, wall materials, caps, steps, guardrails, utility conflicts, engineering, permits, inspections, finish grading, erosion control, and landscape restoration. Height and difficult access can change labor and equipment needs quickly, while a driveway or structure above the wall can change the design itself.

Ask bidders to use the same measured length, retained height, material, drainage route, and restoration assumptions. A low total may omit engineering, excavation spoils, drainage outlets, geogrid, permits, or final grading.

Drainage is part of the structure

Water behind a wall adds pressure and can carry soil through joints or undermine adjacent improvements. A complete proposal should explain how surface runoff is directed, what drainage material and filter separation are used, whether pipe is included, where it exits, and how the outlet will remain serviceable. Do not accept “includes drainage” without a route and outlet.

For warning signs and a deeper explanation of water behind existing walls, see the companion retaining-wall drainage guide.

Permits and engineering vary by address

St. Louis County publishes an official residential retaining-wall guide describing permit-triggering conditions and required plan information. The City of St. Louis residential permit criteria list retaining walls 18 inches or less among work that may be exempt from a residential permit; verify taller or structurally significant walls with the Building Division. St. Charles County states that walls over four feet require a residential building permit, and shorter walls can still require review when they support added loads or have other special conditions. Municipality, zoning, easement, right-of-way, subdivision, and engineering requirements can differ, so ask the authority serving the specific address before design or demolition.

Questions to put in every bid

• Who determined the retained height, loads, soil assumptions, and wall system?
• Is engineered design required, and who supplies sealed plans?
• What excavation, base, reinforcement, drainage, outlet, and backfill are included?
• Who obtains permits, inspections, utility locates, and municipal approval?
• How are property lines, easements, fences, stairs, guardrails, and neighboring grades handled?
• What will be restored, what is excluded, and what written warranty applies?