A retaining wall's job is to hold back soil that wants to move downhill. That soil gets heavier when it's wet, and heavier still when the water in it freezes. Most walls don't fail because the block or stone was weak. They fail because water built up behind them with nowhere to go.
Drainage decides how long a wall lasts
Water trapped in the soil behind a wall pushes against it, and the pressure grows with the wall's height. A well-built wall gives that water a way out:
- Drainage stone behind the wall: clean, crushed stone directly behind the wall lets water drop instead of pressing on the wall.
- Perforated drain tile at the base: a pipe along the bottom collects that water and carries it out past the end of the wall or to an outlet.
- Separation fabric: fabric between the native soil and the drainage stone keeps fine soil from clogging the stone over time.
- Surface water control: grading above the wall so runoff doesn't pour over the top or soak the soil right behind it.
Taller block walls also get geogrid, layers of reinforcing mesh that extend back into the hillside and tie the wall to the soil it's holding.
Block walls or boulder walls?
Segmental block walls use interlocking or pinned concrete units. They build clean, consistent lines, handle curves, corners and built-in stairs, and suit formal or tight spaces. We build block walls with Versa-Lok, and walls over 7 feet with ReCon big block.
Boulder walls use large natural stones fitted together and leaned back into the hill. They look natural, especially on lakeshore and wooded lots, and their weight does much of the holding. They need heavy equipment to set and room to work. Ours are built from Minnesota farmland fieldstone, typically for walls 1 to 6 feet tall.
Either way, structure comes first and looks second. The right choice depends on the wall's height, the site's access, the slope and drainage, and the style of the property.
Design ideas for sloped yards
- Terraces: two or three shorter walls instead of one tall one turn a slope into usable, level space, and shorter walls hold back less soil each.
- Seat walls: a wall at seating height along a patio doubles as built-in seating.
- Curves: curved walls soften a landscape and follow the natural shape of a hill.
- Raised planting beds: tiers make room for gardens at different levels.
- Stone steps: steps built into the wall connect the levels. Our stone steps page covers how they're built.
A real example: a Chanhassen rebuild
At a home in Chanhassen, the original wall was only a couple of courses high, soil had eroded behind it, and the yard sat flat against the house. We removed the old wall entirely and rebuilt it as a five-tier boulder wall, 56 feet long and 42 to 45 inches tall, with a five-foot extension past the original end. Every boulder was set with a mini-excavator and grapple and placed to interlock. Behind it runs four-inch perforated drain tile in a silt sock along the full 56 feet, wrapped in a foot of clean drainage stone, and fresh topsoil restored a positive grade away from the house. A 450-square-foot perennial garden now sits on top. The full project is in our gallery.
Signs a retaining wall is failing
- Leaning or bulging, especially near the middle or top
- Cracks in blocks, stone or concrete
- Blocks shifting out of line, or caps coming loose
- Water pooling at the base or seeping through the face
- Soil washing out through gaps in the wall
- Sinkholes or low spots forming in the ground above the wall
- The slope above moving, with fences, trees or edging tilting downhill
A single sign isn't always an emergency, but signs that get worse each season mean the wall is losing ground.
Repair or rebuild?
A loose cap, a few shifted top blocks, or a clogged outlet is a repair. Leaning, bulging or a wall with no drainage behind it usually isn't, since the problem is in the structure and the soil behind it, not the visible face. In those cases, rebuilding with proper drainage costs less than repairing the same wall every few years.
Permits and taller walls
Taller walls usually need a city permit and an engineered design, and the height where that starts varies from city to city. We check your city's requirements before we build. When a wall needs engineering, we hire an engineer, and for big-block walls the block manufacturer often includes the engineering with the block. Terraced walls are also often a way to get the space you want without one very tall wall.
What a retaining wall costs
Most block walls start around $10,000 to $15,000. Complex walls (multiple tiers, shoreline sites, tight access, heavy permitting) run $25,000 to $50,000+. Boulder walls run about $50 to $150+ per square foot of wall face.