If you’ve been looking for a clean way to create borders on your property, add focal points to your landscape, or create some functionality in your outdoor living area, retaining walls are certainly a crowd pleaser.
However, the biggest question becomes: “how much does this cost?” Well, there are a few things to consider when budgeting for your retaining wall project in the Victoria, BC area. We’ll cover those here.
If you don’t care what goes into building a retaining wall, then you can skip to the average pricing of one here. But there are implications when it comes to making sure it’s built correctly and corners aren’t cut. We want to help you understand how a professionally, well-built wall is built before picking your next contractor based solely on price.
What Goes into Building a Retaining Wall?
To build a proper, long-lasting retaining wall, preparation is key. For a smaller wall under 4 ft that is not under load (such as holding back a driveway or building), you’d need to dig a small trench about 18 inches deep and 12 inches wide. For a larger wall or one that is going to be load bearing, the trench will need to be far wider, 4.5 ft minimum.
This is where we will be putting down geogrid, a special material that uses tensile strength to hold together materials, like rebars in concrete. The width of this trench will depend on the height of the wall. Generally speaking, if there is a building, driveway, or sidewalk within 10 feet of a 4 ft wall, it is considered load bearing.
After compacting the dirt at the bottom of this trench with a plate compactor, permeable fabric will be put down to permit water from draining but prevent dirt and weeds from mixing with the base material. This fabric should extend from the toe of the wall all the way up the back of the trench. 6” of the clear crush will be added and compacted into the trench before the next step.
At this point, the blocks of the wall can go down. It’s important that all the blocks are perfectly level front to back, left to right, and with one another. This will ensure we have a solid level foundation from which all future blocks will be set upon. If this first level has any imperfections, all future blocks placed on top will generally magnify these errors.
A string line should be used to ensure that the line is straight. Once the first course / layer is down, ¾” clear crush gravel is to be put behind the wall and compacted. This ensures good drainage behind the wall as you never want water build up there. Water building up and pushing against the wall is the number one reason retaining walls fail.
The gravel used will allow the water to flow in between the materials down into the ground while the gravel rocks interlock with one another to provide a stable mass behind the wall. If the wall is load bearing or over 4 ft, biaxial geogrid should be used after the first layer of blocks and then ever 2 layers afterwards to ensure maximum stability.
The geogrid should extend from the lip of the blocks all the way to the back of the trench. Geogrid can be found at your local retailers such as Slegg’s. They come in small rows that easily fit inside a sedan and look like a grid of black plastic. A biaxial geogrid is superior to an uniaxial geogrid in that it will resist forces left to right and front to back instead of just one direction. You would then repeat these steps until the wall is at the desired height.
For the very top, a layer of cap stone may be glued on using special adhesives for a nice clean look. Capstones are like little hats for the wall that are flat rectangular pieces. They give a nice finished look to the top of the wall to match the face of the structure you just built.
Fabric should separate the top of the gravel in the backfill area from the 6-12” of top soil which is placed on top. This will prevent the soil from being washed into the gravel, which would cause the material to lose its good drainage abilities. To ensure longevity and prevent erosion from destroying your wall, the top of the wall with the capstone installed should be flush with the top of the surface behind it once completed.
A well-built wall can vary from $35 – $75 per sq ft, where the square footage is based on the face of the wall (so height x length). The variation in prices is based on factors such as if there is machine access, what part of the yard it’s in, whether the wall is load bearing or over 4 ft high, and the overall size with larger walls having a more efficient per square foot cost than smaller ones.
A beautiful wall with two sets of stairs like the one below, which was around 350 sq ft including the stairs, would be about $14,000 to $16,000. Stairs generally tend to increase the complexity of a project, but also the value that’s added to your property.
A boulder wall such as this, which was around 80 sq ft, would cost around $3200 – $3800.
A small gardenscape wall like this, around 40 sq ft, would cost around $1800 – $2000. Mulch and plants could add an extra $500 – $1000 to the cost depending on the complexity of the plants and shrubbery.
A retaining wall of this size below (around 100 sq ft) is going to be about $4000 – $5000. It’s in the backyard, which makes access difficult and the hill is quite steep. If additional soil is needed to be brought in to level the yard, that would also be extra $500 – $1000.
The number one reason retaining walls fail is due to improper construction and drainage. When the wrong gravels are used, the base can shift, causing the wall on top to lean and topple. If a terrace is involved, walls must be separated by a minimum distance between terraces or there will be insufficient strength in the walls to resist the extra loads.
If there is no fabric used or dirt is used to fill the space behind a wall, hydrostatic pressures resulting from the inability of the backfill to drain will cause the wall to blowout. These and many more reasons are why it is recommended that a professional do this and do it properly.
Best case scenario, your expensive wall looks great for the first year but then starts to lean and then fail within the next 2-3 years. Worst case scenario, whatever your wall was holding up (such as a shed or driveway) slides down the hill and buries whatever is below it causing massive property damage.
With the wet winters we have here in Victoria, it is especially vitally important that walls are built properly and with proper drainage.
We Hope this Helps!
After reading this, we hope this gives you a good idea of how much different retaining walls may cost depending on your needs and application. If you’re looking for a more accurate cost, we can provide you a free estimate.