Retaining walls are used to control backfill and topsoil and prevent them from eroding. Retaining walls can be built from stone, formed concrete, cement blocks, or rot resistant wood, like pressure treated timbers. Today we will discuss the most economical ways to build a retaining wall and how to start.
What Is a Retaining Wall?
A retaining wall is an outdoor feature of landscaping that secures or retains soil, preventing erosion. Retaining walls are common along interstate highways to prevent nearby hillsides from crumbling onto the road. Retaining walls are also used in residential landscaping where driveways or other features have been cut into a hillside. Retaining walls can be part of an erosion prevention system when combined with vegetation, drains, and other landscaping features.
What Is the Easiest Retaining Wall to Build?
In most situations, a DIYer can install a small (less than 36” tall) retaining wall using landscape timbers. Landscape timbers are often confused with pressure treated 4 x 4s, but they are not the same. Landscape timbers are lower grade lumber and primarily used for their strength, not their appearance.
Landscaping timbers are rounded on the corners to resemble logs when stacked together. Long, corrosion resistant spikes are driven into both the ground and the timbers to prevent separation of the wall. However, because landscape timbers are only 3” x 4” wide, they cannot provide support to retaining walls over 48” (4’) tall. Taller retaining walls should be built from masonry materials.
Can I Build a Retaining Wall Myself?
Yes. Depending on your experience with masonry and woodworking, you can probably build your own retaining wall. As mentioned previously, most do-it-yourselfers will have the tools and skills to use landscape timbers to construct the wall. If you have experience working with concrete, you can probably also build a retaining wall with concrete blocks, or interlocking cement blocks.
What Is the Cheapest Way to Build a Retaining Wall?
Here we will discuss the least expensive ways to construct a retaining wall and the pros and cons of each, arranged from least expensive to most expensive.
As mentioned earlier, the easiest retaining wall for a DIYer to install is likely a landscape timber wall. Fortunately, it is also one of the cheapest types of retaining wall because the only materials needed are the timbers and a few spikes. Landscape timber retaining walls can be built quickly and only require a few common tools a do-it-yourselfer will often have, like a saw and hammer. Landscaping timbers are also pressure treated, so they can lay directly on the ground without rotting.
Cost: About 12.00 -15.00 per square foot
Natural stones, like slate and river stones can also be used to build an effective retaining wall. From a cost standpoint, a natural stone retaining wall can be the cheapest version if the stones can be collected. Natural stone retaining walls use mortar and the weight of the stone itself to resist the force applied by the backfill. A natural stone retaining wall can be any thickness, but unless rebar is also used, it should be at least 250mm thick, or about 10” minimum.
If the goal is to collect stones for the wall, stone selection will affect the installation. For example, some natural stone walls like those that use slate, will generally require less mortar, but more stones. River rocks and other more rounded stones will use fewer stones because they are usually larger and take up more space. So, it is important to note that selecting the appropriate stones will affect both the labor and materials needed to complete the project.
Cost: Free – 30.00 per square foot
A concrete block retaining wall is one of the most common versions because it is simple and relatively inexpensive to build. Because concrete blocks are available in various sizes as well, they are a versatile option, especially when filled with concrete and/or rebar. Building a concrete block retaining wall can be a DIY project, but the labor required can be significant. Retaining walls built from concrete blocks will also require a concrete footing, adding to the total cost.
Cost: About 20.00-30.00 per square foot.
Interlocking Concrete Blocks
Interlocking concrete blocks use the force applied to the wall to interlock each block to the next, forming a solid unit. Interlocking concrete blocks contain a lip along the bottom rear edge of each block, providing support to both blocks with the goal of eliminating the need for mortar. Interlocking retaining walls not using mortar and can be used for a retaining wall up to about 30” tall. However, this method will require site preparation and additional materials, like sand.
Interlocking concrete blocks are similar to paving stones in the way they are installed. In most instances, a very fine sand is laid as a footer and the stones’ weight imbeds the stones into the sand. Then additional blocks are laid as specified by the manufacturer up to the recommended height. Interlocking concrete blocks are easy to work with and simple to install, but depending on the application they can be as expensive as poured concrete.
Cost: About 20.00 25.00 per square foot
Pouring a solid concrete wall will result in the strongest retaining wall, but will also be among the most expensive. Excavation and labor represents over 50% of the expense in a poured concrete retaining wall, so larger walls can be costly. Poured concrete walls can also be reinforced with rebar or other structural steel, allowing them to rise as high as needed.
Cost: About 25.00-40.00 per square foot
A very common retaining wall option uses stacked railroad ties. Railroad ties are very rot-resistant (like landscaping timbers), but they should be handled with care and skin protection. Railroad ties are rot and insect resistant because they contain a chemical called creosote, which can cause skin burns.
Railroad ties are installed by digging a trench slightly larger than the tie, and placing it into the hole as a footing. Subsequent ties can then be nailed (using railroad spikes or other large fastener) together for strength. Railroad tie retaining walls can be built up to six feet high (72”) but should be reinforced with rebar if they exceed four feet (48”).
Cost: About 25.00 – 30.00 per square foot.
Build the Wall For Strength
Obviously, we want a retaining wall to look good, but it is important to satisfy the need for strength. The pros will always design a retaining wall first for strength, and then for appearance. If you need help designing a wall you can build, speak to a structural engineer and have them design your retaining wall. The goal is to solve your erosion concerns the first time, so do your research and if needed, ask a pro.