Cost of a Retaining Wall
With such variation in the method and materials of retaining wall construction, actual costs can be difficult to assess without a completed design. Fortunately, walls below 4' that do not require special engineering and are composed of a CMU block core with attractive veneer are relatively uniform in their cost of construction. In this application, which includes seatwalls, it's the veneer itself that dictates the ultimate cost differential.
- Pro Tip: When it comes to retaining walls, don't be a do-it-yourselfer.--James Woodhead of Woody's Custom Landscaping in Battle Ground, WA
Landscape Architect, Marco Romani explains: "We've replaced a lot of walls where the original contractor failed to use gravel or used too little gravel behind the wall. In just two years those walls are covered with efflorescence (a moisture induced white mineral residue). We insist on being generous with drainage materials to make sure our walls last. Lots of washed gravel is so important. We apply a 2 foot thick layer of gravel immediately behind the wall, and this may be even wider for more expansive walls. That's why our stone veneer walls run from $190 to $250 per linear foot."
This demonstrates how costs can often be lower due to failure to address the most important part of a retaining wall: drainage structures. Moisture may originate deep underground too, wicking up through the concrete footing. "Moisture is the primary concern for us with all our masonry. Water always finds its way out. When a seatwall is a planter wall, it's always getting wet. To prevent wicking we use a rubber flashing at the base of the foundation that cuts moisture off from concrete footing so it doesn't suck up into stonework." Romani produces some of the finest stone veneer retaining walls in the Chicago area and knows the danger posed by extreme climates.
No matter what kind of wall you build, however, there are some universal factors that can constitute hidden costs.
What Affects the Cost of Retaining Walls: Location - Areas of extreme weather or earthquake risk may demand greater structural reinforcement and more extensive waterproofing.
Spoils - Larger walls or those with extensive engineered footings will require a great deal of excavation. In some cities, the removal of spoils can drive up costs considerably as does the demand for a great deal of fill behind a wall.
Material cost - Stone veneer that requires a stone mason to fit it adds higher labor costs to the bottom line.
Soils - Areas of expansive soils or bedrock can drive up excavation costs and foundation size.
Steps - Adding steps or pilasters to a retaining wall can increase the wall cost exponentially.
Access to building site - A site where masons and deliveries can be made to the location of the wall is less expensive than one where materials must be hand carried due to narrow sideyards and limited backyards.
Fill material - Topsoil is brought onsite to fill the back side of a retaining wall against the slope, or where raised planters with retaining walls need to be filled. Limited access can require extensive labor compared to a simple dump and fill.