A retaining wall resists the lateral pressure of soil to prevent slope failure. They're essential for landscaping, driveways, foundations, and hillside construction.
Types
- Gravity wall: Uses its own weight to resist soil pressure (stone, concrete)
- Cantilever wall: Reinforced concrete L-shape, most common for 4–25 ft heights
- Sheet pile: Interlocking steel sheets driven into ground
- Anchored wall: Cables or rods anchor wall to rock/soil behind it
Design Rule of Thumb
Base width ≈ 50–70% of wall height. Walls over 4 ft typically need engineering and permits.
Drainage Is as Important as the Wall Itself
Most retaining wall failures aren't caused by insufficient wall strength — they're caused by water pressure building up behind the wall with nowhere to go. Proper design includes a gravel backfill zone, a perforated drain pipe at the base, and weep holes, all working together to relieve hydrostatic pressure that would otherwise push the wall over.
When You Need an Engineer, Not Just a Contractor
Most jurisdictions require a stamped engineering design and permit for retaining walls over 4 feet tall, or any wall supporting a surcharge load (like a driveway or structure above it) regardless of height — the consequences of an undersized wall failing are severe enough that this isn't a step worth skipping.