Concrete retaining walls add structure in hilly areas, protect homes or gardens from encroaching land, create terraces for gardening or lawn design, control erosion, control water runoff, and look great. Concrete is made from mixing water with portland cement, sand and gravel. When the mixture dries, it forms a strong, pressure-resistant solid that withstands weather and heavy weights—perfect for holding back soil. When building a retaining wall, most states require that an engineer is involved if the wall will be taller than four feet. Local building codes may have their own regulations, so it’s a good idea to plan ahead before building.

Prior to installation, concrete professionals consult on design, prepare the land by grubbing (removing trees, shrubs and other obstacles) and leveling the location of the retaining wall. The amount of labor required affects the total project cost. Depending on the type of concrete retaining wall, the base is created first. Common wall styles include cantilever retaining walls, counterfort retaining walls, gravity-poured retaining walls and semi-gravity retaining walls. Several factors affect overall project costs.

Square footage

Concrete installation professionals often provide a price per square foot. Henry Fuapau of 4Sons Concrete in Portland, Oregon, says his company’s per-square-foot pricing—$23 to $28—includes excavation (preparing the land for the retaining wall), materials, steel reinforcement and framing. Prices vary based on design, install location, cost of labor in the region and complexity of the project.

Stack walls

Stack-block concrete retaining walls are a stylish alternative to installing a poured concrete retaining wall. Made of prefabricated blocks, they are perfect for lower-scale projects such as slightly raised garden beds, retaining lower levels of earth and creating definition in hardscaping. Here’s a project cost example from 4Sons Concrete for a large-scale stack-block retaining wall:

• 100-foot-long, three–tier, summer-blend stack concrete wall tapering from 3.5–feet down to 2-feet-high: $15,000

  • The overall project also included 30 yards of concrete patio (three separate patios), concrete stairs down both sides of the house and a concrete BBQ area, which came to 500 total square feet of concrete: $20,000

  • The retaining stack wall would have been $20,000, but the customer received a $5,000 discount for bundling the patio work with the 100-foot retaining wall work.

Height

Concrete walls over 4 feet high require the planning and oversight of an engineer to meet building codes. Typically an engineer works separately from the concrete installation company, and the planning is an additional cost in the overall project. Some engineers charge an hourly rate—an average is $100, which can increase or decrease by as much as $50 or more, depending on the geographic region and the engineer’s experience. Also, higher retaining walls involve a multipour process instead of one concrete pour, which requires added materials and labor, increasing the total project cost.

Recycled concrete

Eliminating the need for new materials can help reduce retaining wall project costs. Fuapau of 4Sons Concrete says they can build a retaining wall using recycled concrete taken from other projects or even concrete that’s been demoed at the current project site. Most concrete companies offer a reduced rate for recycled concrete because they save on materials and dumping fees. Here’s a project cost example from 4Sons Concrete for a retaining wall made from recycled concrete:

• Recycled-concrete retaining wall: $12–$20 per square foot, depending on project site and wall design

  • Demolish 30 yards of driveway and build an 8-yard recycled-concrete retaining wall: $5,000—approximately $2,500 savings over using new concrete

  • This customer wanted 20 yards of driveway removed and needed 8 yards of retaining wall built in the garden. 4Sons Concrete didn’t have to haul out or pay disposal fees on the concrete used in the retaining wall, saving on labor and transportation costs as well.

Design

The cost for a concrete retaining wall increases with more curves, steps and other special elements in the design. Curves and nonstandard designs need special framing, which requires more labor and materials. Cement contractors often build steps into a retaining wall to serve as backyard or garden seating. This type of project is more work and, thus, costs more than a standard wall. 4Sons Concrete charges an extra $16–$18 per square foot to handle the additional design work and add the steps to a wall.

Reinforcement

The amount of reinforcing steel (often called "rebar") needed in a retaining wall affects the overall cost because of the added material and labor. However, this additional structural support may be needed for walls taller than 4 feet high or those holding back significant weight.

Accessibility

The harder it is to access the installation site, the higher the labor costs will be. When contractors can pull trucks and heavy machinery straight to the location, they save time, money and people power. When hand-hauling equipment and concrete to the site is necessary, the price increases.