Updated April 13, 2023
Retaining walls are a popular landscaping feature, especially for homes sitting on sloped or uneven land. Some retaining walls are structurally necessary, others are purely for looks. Whatever their purpose, retaining walls come in infinite shapes, sizes and styles. That, plus the fact that they can be extremely complicated to build, makes them a bit daunting for many homeowners.
But never fear! We’ve created this guide with everything you need to know about planning, building, and maintaining retaining walls.
A retaining wall is a wall meant to hold back earth on one side, thus keeping the ground at different levels on either side of the wall. It retains the soil behind it, thus the name.
Retaining walls are used all over the world for an incredible number of purposes. They’re used along roadways, especially through hilly terrain. They’re used for agriculture, like the iconic rice terraces seen across Asia. They’re used along urban coastlines, where they’re known as seawalls.
And they’re used in the yards of many people’s homes to re-shape sloped land.
Why would someone want to re-shape their property?
Often, it’s to increase the usable space. If your house is built on a steep hill, you may find that you have no room for a patio. A retaining wall can level off a section of the property so you can fit a patio or a pool or another structure.
Another function of retaining walls is to control drainage and erosion. Properties located on slopes may suffer from soil erosion. Soil erosion occurs when rainwater or melting snow washes away the surface soil. This can cause many problems, like wearing channels into the land or washing earth away from the home’s foundation. Retaining walls help control the flow of draining water.
It may not be obvious when looking at them, but retaining walls are under extraordinary pressure; even small walls may be holding back hundreds of tons of earth. Accordingly, they’re usually designed by professional engineers.
There are two ways we can divide the different types of retaining walls: by the method of their construction, and by the materials used to build them.
On the method side, there are many ways to build a retaining wall. The most basic is the gravity wall, which is simply a wall holding back earth. These are normally only used for short walls, as they lack the extra reinforcement of other types.
There are also cantilever retaining walls, which are L-shaped. The bottom of the L extends backwards from the wall, so the retained soil weighs it down and provides extra reinforcement.
Next are sheet piling walls, which consist of a series of posts, or pilings, driven deep into the ground and used to support a sheet of steel, wood, or other material that holds back the soil.
Another common type is anchored walls. Anchored retaining walls have many long anchors extending through the wall deep into the soil behind them.
Most homeowners, however, are probably more concerned with what the wall looks like than how it’s built. The appearance is mostly based on what material the wall is constructed from. There are many options, but here are the most common (along with their pros and cons):
|A durable material that can last a long time
|Most walls require professional design for the support structures.
|Very low maintenance
|Labour for installation can be expensive
|Plenty of style options available
|Can’t support a tall retaining wall
|Very pleasant, natural appearance
|Prone to rotting and pest infestations
|Easy to install
|Can’t support large retaining walls
|Challenging installation that almost always requires professionals
|Can be crafted into nearly any form
|Susceptible to frost and moisture damage
|Beautiful, classic appearance
|One of the most expensive materials
|Needs carefully-designed drainage
|Very labour-intensive installation
|Resistant to the elements
|Limited colour availability
The type of retaining wall you choose is partially dependent on the needs of the installation site. For example, a very tall wall that’s holding back a lot of earth might preclude the use of some materials like cinder blocks or wood. This is one of the reasons it’s usually necessary to engage the services of a professional engineer when designing a retaining wall.
Once they’re installed, retaining walls are fairly hands-off (especially if they’ve been designed and built properly). That said, there are a few things you need to be aware of if you have retaining walls on your property.
Whatever material your walls are built from, you’ll want to inspect them regularly for signs of wear, especially in the spring. For concrete or mortared walls, be on the lookout for cracks, especially if you live in a climate with freezing weather. Cracks are common signs that moisture has penetrated the wall and frozen. If caught early, it may be possible to mitigate the problem. But, if you let it persist, you’ll find that the whole wall starts to lose its integrity and will need replacement—a costly proposition.
Drainage is another issue to be alert for. If the soil behind the wall gets saturated with water and can’t drain, it’s weight may become too great for the wall to bear. Water is heavy! In extreme cases, it may burst through the wall and cause a miniature landslide.
If your retaining wall has drainage pipes built into it, make sure they’re kept clear without the year. If you find that your drainage problems are chronic in nature (as in, they don’t go away), you may have a lot of work on your hands.
You’ll need to bring in a professional to diagnose the cause of the drainage issues and design a solution. Solutions to ongoing drainage problems can involve digging and re-grading the land around the wall, removing subsurface soil and replacing it with gravel, or installing drainage tiles. None of these are easy, but they’re probably better than watching your retaining wall collapse.
Another reason it’s good to have your retaining walls professionally designed: drainage issues are best managed before the wall is even built.
If your drainage problems are slight, you might be able to mitigate them by planting some greenery above the retaining wall. They’ll pull a little water out of the ground, and their roots will also help stabilize the soil. Just don’t plant large greenery (like trees) too close to the wall, as their roots may damage it.
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How long a retaining wall lasts depends on three things: what it’s made of, how well it was built, and how harsh its environment is. This can make it hard to estimate how long they’ll last.
Let’s assume the wall was designed and built well. A concrete wall should last 50-100 years. Brick or stone masonry walls can last even longer—there are retaining walls built during the days of the Roman Empire that are still hanging around. Wood retaining walls have a shorter lifespan, lasting up to 40 years but more likely just 10-20 years. A gabion retaining wall can last 50-100 years, especially if it’s metal wiring isn’t exposed to wet coastal air.
Often, your home insurer won’t need too much specific information about your retaining walls. They will, however, need to know if you have them, and how much it would cost to replace them.
Retaining walls are normally not part of the coverage for the house itself. Some home insurance providers consider retaining walls to be detached structures, meaning they share a category with sheds, gazebos, and docks. This coverage is commonly called “Coverage B.” Often, insurers give property in this category an automatic coverage limit equal to 10% of the main building’s coverage limit.
In Square One’s case, we include retaining walls in the Detached Structures, Fences and Landscaping coverage. This is a completely optional coverage that customers can add to their policy if they need it.
If you’re not sure how your insurance provider categorizes retaining walls, make sure you ask them so you’re clear.
In any case, you need to estimate the replacement cost of your retaining walls to decide how high a coverage limit you need for them. To do so, estimate the cost of materials and the cost of labour involved in replacing them, and add the costs together.
Whether your home insurance covers a damaged retaining wall or not depends on what caused the damage.
Home insurance doesn’t cover regular wear and tear, nor faulty installation. So, if your retaining wall wasn’t installed properly, or hasn’t been maintained well, home insurance won’t cover any resulting damage.
If you had a professional contractor build your retaining wall, they would be responsible for any faults in the construction. As the homeowner, you’re responsible for routine maintenance, so make sure you’re staying on top of frost damage, drainage problems, and other potential issues.
Home insurance will often cover damage from sudden and unexpected events, though. If your wall is damaged in a fire, or struck by an errant vehicle, your home insurance should pay to repair it.
Home insurance policies normally do not cover damage from flooding or earth movement (landslides or earthquakes), both of which could cause severe damage to a retaining wall. Another reason to ensure your wall is well-built and well-drained.
Most policies sold by Square One do include coverage for earthquakes and inland flooding, however. If your policy has these coverages, it will extend to your retaining walls as well.
It can be hard to decide the best way to use a retaining wall on your property. After all, there are basically infinite options for designs and styles. The type of material you choose will depend largely on what looks good with your house and yard, of course.
For some inspiration, here are some non-standard retaining wall ideas:
A retaining wall is, after all, a wall. Adding some steps in the middle makes it possible to traverse the wall without having to do a lot of awkward climbing.
Rather than a single, tall wall, think about separating it into tiers. This can add a ton of visual appeal to your property, plus make it easier to install; short tiers may not need as much input from engineers or other contractors (if you’re looking to DIY your walls).
If you’ve made the investment to have a beautiful stone retaining wall, why not show it off? Especially if you’re planning on building a patio on or near your wall. Speaking of which…
Retaining walls are often used to flatten out space for a patio. They can also become part of the patio itself—great to combine with the multi-tiered approach.
Who doesn’t want a calming backyard waterfall? A water feature built right into the wall really increases the visual appeal.
Most properties don’t need a retaining wall. They’re often added purely for visual appeal or to create more level space for a patio or pool.
You may need retaining walls, though, for a couple of reasons:
If you live on a steeply-sloped property, you may find that soil erosion is an issue. As water runs down the steep slope, it carries earth with it. Eventually, this might start to expose your home’s foundation, or dig deep water channels into your yard. Leveling things off with retaining walls helps control the water drainage and the erosion.
As well, if your property is prone to flooding, carefully-designed retaining walls can help channel flood water away from the building.
Small retaining walls are often DIY-able, but still require that you know what you’re doing. Even a 1-metre-tall wall might be subject to dozens of tons of pressure.
More often than not, a retaining wall needs to be designed by a professional geotechnical engineer. An engineer can create the right design for the size and stress and ensure that the wall has good drainage—both absolutely critical.
“The general rule of thumb in the construction world is that a retainer wall over four feet tall should be left to the experts,” says Shane Dutka, Founder & General Manager of Review Home Warranties. “Given how structurally important they are, and how expensive a mishap is, I advise going with a professional to plan and install your retainer wall. It’s worth the cost just from a safety standpoint.”
Because retaining walls vary so much in size, length, and design, it can be difficult to estimate the cost. Often, the price is calculated based on square-footage; that is, the surface area of the wall’s face. As a rough estimate, you’re looking at $25-35 per square foot at a minimum to cover materials and labour. So, a wall that’s 4 feet high and 20 feet long would start at about $2,000.
Of course, that can easily skyrocket to $10,000 or more if it’s a large or complicated project.
If you’re hiring a professional engineer to design the wall (generally a good idea), adding 10% to the price is a reasonable estimate.
Retaining walls are subject to the usual liabilities of home ownership. For example, if your patio sits atop a large retaining wall and someone falls off and injures themselves, you could be liable for those injuries (you should have installed a railing).
Where it gets complicated, though, is when neighbouring properties get involved.
If your retaining wall collapses and causes damage to a neighbouring property, you could be held liable for that damage, too (or the contractor that built the wall, if faulty construction is to blame).
Issues also arise with retaining walls that straddle property lines. Typically, whoever has the wall on their side of the property line is responsible for any liability issues. But, sometimes, a retaining wall on one property is actually holding earth belonging to the neighbouring property.
Disputes over retaining walls often wind up in court.
If you’re building a new one anywhere near your neighbour’s property, make sure you’ve crossed your t’s and dotted your i’s: get your building permits, make an agreement with your neighbour, and get the property line surveyed.
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