Retaining walls are used to control backfill and topsoil and protect them from erosion. Retaining walls can be built from stone, concrete, cement block or rot-resistant wood, such as pressure-treated lumber. Today we’ll discuss the most economical ways to build a retaining wall and how to get started.
What is a retaining wall?
A retaining wall is an outdoor feature of landscaping that secures or holds soil, thereby preventing erosion. Retaining walls are common on interstate highways, to prevent nearby hills from collapsing onto the roadway. Retaining walls are also used in residential landscaping, where driveways or other features are cut into the hill. 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” high) 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 low-grade lumber and are used primarily for their strength, not their appearance.
Sticks for landscaping are rounded at the corners so that they look similar to logs when put together.
Retaining wall in the garden
Image credit: Canva
Long, corrosion-resistant nails are driven into both the ground and the wood to prevent the wall from coming apart.
However, since landscape timbers are only 3” x 4” wide, they cannot support retaining walls taller than 48” (4′). Taller retaining walls must 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 earlier, most do-it-yourselfers will have the tools and skills to use landscape timbers to build a wall. If you have experience working with concrete, you can probably also build a retaining wall with concrete blocks or interlocking cement blocks.
Here we’ll discuss the most expensive ideas for retaining walls and the advantages and disadvantages of each, ranked from least expensive to most expensive.
Landscape Timbers
As mentioned earlier, the easiest retaining wall for a DIYer to build is probably a landscape timber wall. Fortunately, this is one of the cheapest types of retaining wall because it only requires wood and some spikes. Landscape timber retaining walls can be built quickly and only require a few common tools that a DIYer often has on hand, such as a saw and a hammer. Landscaping timbers are also pressure treated, so they can be laid directly on the ground without rotting.
Cost: Approximately $12–$15 per square foot
Natural Stone
Natural stones such as slate and river stones can also be used to create an effective retaining wall. From a cost perspective, a natural stone retaining wall can be the cheapest version if the stones can be sourced. Natural stone retaining walls use mortar and the weight of the stone to resist the force exerted by the backfill. A natural stone retaining wall can be any thickness, but unless rebar is used, it should be at least 250 mm thick or about 10 inches minimum.
If the goal is to assemble stones for a wall, the selection of stone will affect the installation. For example, some natural stone walls using slate will generally require less mortar, but more stones. River stones and other more rounded stones will use fewer stones because they are generally larger and take up more space. Therefore, it is important to note that selecting the appropriate stones will affect both the labor and materials needed to complete the project.
Cost: $0–$30 per square foot
Concrete Blocks A
concrete block retaining wall is one of the most common versions because it is simple to build and relatively inexpensive. Since concrete blocks are also available in a variety of sizes, 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 considerable. A retaining wall made of concrete blocks will also require concrete footings, which will increase the overall cost.
Cost: Around $20-30 per square foot.
Interlocking Concrete Blocks
Interlocking concrete blocks connect each block to the next using the force applied to the wall, forming a solid unit. Interlocking concrete blocks have a lip on the bottom rear edge of each block, which provides support for both blocks, with the aim of eliminating the need for mortar. Mortar is not used in interlocking retaining walls and can be used for retaining walls up to about 30 inches high. However, this method will require site preparation and additional materials such as sand.
Interlocking concrete blocks are similar to paving stones in the way they are laid. In most cases, a very fine sand is laid as a footer and the weight of the stones presses the stones into the sand. Additional blocks are then laid to the recommended height specified by the manufacturer. 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: Approximately $20–$25 per square foot
Poured concrete
A poured concrete wall will make the strongest retaining wall, but it will also be the most expensive. Excavation and labor represent more than 50% of the cost of a poured concrete wall, so large walls can be expensive. Poured concrete walls can also be reinforced with rebar or other structural steel, allowing them to be raised as high as needed.
Cost: About $25–$40 per square foot
Railroad ties
A very common retaining wall option uses stacked railroad ties. Railroad ties are very rot-resistant (like landscaping lumber), but they must be handled with caution and skin protection. Railroad ties are rot and insect-resistant because they contain a chemical called creosote, which can burn skin.
Railroad ties are installed by digging a trench slightly larger than the tie and placing it in the hole as a footing. Subsequent ties can then be nailed together (using railroad spikes or another large fastener) for strength. Railroad tie retaining walls can be built up to six feet high (72”), but must be reinforced with rebar if they are higher than four feet (48”).
Cost: Around $25-30 per square foot.
Build a wall for strength
Obviously, we want a retaining wall to look good, but it’s important to meet strength requirements as well. Professionals will always design a retaining wall for strength first and then for appearance. If you need help building a wall, talk to a structural engineer and ask them to design your retaining wall. The goal is to solve your erosion concerns the first time around, so do your research and, if necessary, ask a professional.