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A retaining wall that can't properly drain water is heading right for collapse.
A retaining wall that can't properly drain water is heading right for collapse.

A retaining wall may be a small part of your yard, but it’s got a big job to do. Retaining walls hold back a lot of heavy soil in areas that feature a steep difference in height. Often, you might see retaining walls near your neighbours’ swimming pools, driveways, or multi-tiered gardens. Any spot where there’s a sudden shift in the landscape, where you wouldn’t want a ton of excess soil to tumble — that’s where you’ll find a retaining wall.

Retaining walls can be made with all sorts of materials, from poured concrete, to treated lumber, to rocks and stone. While they can provide some nice curb appeal, choose your material based on your needs and its longevity. A retaining wall that fails because you chose the wrong material, or had it installed poorly isn’t going to do you any good.

So what are some of the common problems with retaining walls and how do you address them?

No drainage

I say it again and again: even a little bit of water can cause big damage to your home. That extends to your outdoor structures like decks, sheds, and retaining walls. You’d think that a structure that’s meant to be outside in the elements should be naturally resistant to water, right? Well, not if it’s built wrong.

When you’re planning a retaining wall with proper drainage, it’s important to know what type of soil you have. Clay soil is very compact, and so it won’t drain as well. But it’s less vulnerable to erosion — a bonus! Sand is more porous and well aerated, so it drains well, but it’s prone to erosion.

When too much water gets into the soil surrounding the retaining wall, without the ability to properly drain, it gets heavy with water and can start to put too much pressure against the retaining wall, causing it to fall away. In Canada, especially with our freeze-thaw cycle, you’ll see that water-filled soil start to expand and contract, ultimately pushing the wall over.
So how do you keep water flowing? Regrading the slope of the yard can help promote water movement. And installing a proper weeping bed using materials like crushed gravel allows water to drain along the bottom of the wall.

Poor foundation

A retaining wall with a bad foundation will topple or collapse. How do we avoid that? You’ll have to place the footings keeping in mind that they need to be deeper than the frost line — and that needs to be measured from the lowest part of the grade. If you don’t do that, the wall will move up and down as the ground freezes and thaws — coming loose over time.

It also needs to be strong enough to withstand the weight you put against it. Your wall will be designed to retain a certain load and if you exceed that, it might collapse. How do we solve that? Be very clear with your landscape architect about how you intend to use the retaining wall. If it needs to also support the weight of a patio set, let them know. You can strengthen your wall by installing anchors, or pouring concrete to create a thicker base but this is something you’ll want to do before you finish the wall.

Does it fence you in?

A few years back we did a major backyard overhaul for some homeowners that included a few staggered retaining walls. It was a large property with a heavy slope that required walls at several levels to keep the soil back.

Now, it’s not just about looking good it’s about doing it right. And in this particular job, our retaining walls also required guardrails for safety. Yours might too. After a certain height you may be required to add one.

Check your local building code to see at what height guardrails are required. Don’t skip this step. Of course, even if your fence doesn’t meet the height necessary to require a barrier — think about your personal needs. Do you have young kids running around your yard, or a retaining wall that overlooks a swimming pool? It may be worth peace of mind to add one anyway.

Watch Mike Holmes in his series, Holmes Makes It Right, on HGTV. For more information, visit makeitright.ca .

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