A retaining wall is a common structure in landscaping to make better use of a slope or create a decorative statement. Depending on its purpose, a retaining wall can be very short or very tall. With proper retaining wall drainage and construction, it can bring a lot of character and function to your landscaping.
Retaining walls are a seemingly simple enhancement to any landscaping project. However nearly 80% of all residential retaining walls fail at one point or another because of poor drainage. Retaining wall drainage is the most important aspect of its structure. But many times, drainage is often eliminated to reduce the cost of the project.
If water and soil find their way into the structure of your retaining wall, it can quickly create a disastrous outcome. This damage could potentially destroy all of your hard work. For this reason, you should consult a professional very thoroughly before starting on any retaining wall project.
On level ground, create an elevated planting area with a stylish and practical retaining wall. This will provide improved drainage while creating a place for seating. With proper retaining wall design, you can build a long-lasting and functional structure. These additions will add value to your home or business.
What is a retaining wall?
Retaining walls are very versatile and uniquely designed structures that hold soil on one side and are free-standing on the other. This type of wall can help you work with uneven topography and changes of grade in a landscape. Proper retaining wall design and construction can help:
- Make usable space out of a steep slope
- Provide a place for landscape plantings
- Create a level area for a driveway.
Retaining walls are made out of variety of materials such as wood, stone, brick, or concrete. They provide extra support in preventing soil from moving. Specific reasons for using a retaining wall will depend on the project. Typically, you use retaining walls to hold back earth to create level landscapes or prevent erosion. Projects can range from small landscape walls to large walls along a roadway.
Although a retaining wall may seem like a fairly simple structure that anyone can put together in an afternoon, it is far from simple. Designing and constructing a retaining wall that withstands the test of time requires someone with the knowledge of lateral earth pressure. This is the pressure developed by backfill.
Some people believe a retaining wall is merely an arranged pile of blocks. But don’t be fooled. A retaining wall is an engineered system that often uses gravity to hold back the earth! So not surprisingly when they fail, you have a problem. They can pose a serious risk to human safety and be a hazard to your property. That’s why it’s important to call on an expert to build your retaining wall.
Retaining wall design and drainage tips
A variety of important considerations go into the planning of a new retaining wall. You first have to decide the height and length of your wall and where you will build it. The wall must be the proper height for its location on the slope. It must also have properly compacted backfill, a suitable base and efficient drainage. If you leave out any of these important elements, you may end up with a wall that fails, collects water or is unsafe.
Suitable Base and Foundation
Retaining walls can be extremely heavy, compressing the soil underneath. As a result, the wall could shrink because there may not be enough pressure to keep it upright. At this point, your entire wall will fail.
The base of your retaining wall sets the stage for the finished project. You should start with a suitable base material that is both solid and level. If possible, use soil that has not been used in a landscape environment before this project. This type of soil is sturdier and better suited to supporting a retaining wall.
Your excavation contractor should dig the base well below the grade and then add a solid and level foundation. By starting with a level foundation, you can avoid having to use shims that take more valuable time and can reduce the structural integrity of your wall.
Use backfill properly
The backfill of your retaining wall is just as important as the wall itself as it provides the proper drainage. If not, the wall will fail. It is very important that backfill is at least 12 inches of clean crushed stone. Beyond this point, it is completely ok to use compacted soil extracted from the area where you are doing the project. If you have plans to landscape behind the wall, use at least six inches of native soil over the gravel backfill.
Your contractor(s) should take the steps necessary to ensure that the backfill is structurally sound and properly compacted. They should backfill your wall as they go, filling it in at 8, 10 and 12-inch increments against the wall. To prevent sunken areas appearing in your backfill after you finish the wall, your contractor should thoroughly compact each layer.
Tip: Don’t use dirt as backfill. The dirt will retain water and will not drain properly. This situation will add additional pressure to the back of the wall.
Lay perforated piping
In addition to the foot of backfill used behind your retaining wall, you should also make sure that perforated piping is laid at the bottom of the backfilled portion of the wall. This helps create a hollow channel for water to go in the event of a heavy rain or watering. This piping diverts the water away from your retaining wall. Then you won’t have to worry about it collecting behind the wall, causing pressure and decay.
Install weep holes
Another important aspect of your retaining wall drainage plan is to have properly installed weep holes. Work with your landscape construction expert to ensure that these holes are the right size and appropriately placed to ensure that any excess water can drain through the wall. This will essentially give any moisture an additional route away from your wall, which is your ultimate goal.
Proper height and reinforcement
Height is an important aspect of your retaining wall. As a rule, you can build most retaining walls up to a height of 4 feet without having to add additional supports or tiebacks. If you are building anything taller than this, additional reinforcement is necessary. And you may possibly need building permits.
It’s critical to properly reinforce your retaining wall so it’s strong and secure. Typically, contractors use a rebar as reinforcement. A rebar is a steel bar used in construction to add weight.
Ensure you install the rebar correctly. Otherwise, the wall may separate at the corners. As always, that’s why it’s important to hire an expert for this type of project.
Invest properly for a long-lasting retaining wall
A retaining wall project is a major investment in both time and money. Because of this, make sure that you don’t make one of the most common (and most destructive) mistakes that any homeowner can make: cutting corners in the project and eliminating proper retaining wall drainage. By spending a little bit of extra time and a few more dollars on the project, you can ensure that your wall drains properly and will remain in place for many years to come.
I am glad that you brought up weep holes. I have been thinking about installing a timber retaining wall in my backyard this spring. But I haven’t thought at all about how rainwater will travel throw the wall. It seems like I should talk to a landscaper about how best to do that for the type of wall I want.
I’d love to get a retaining wall installed in my backyard, so it’s helpful to know that proper water drainage is essential for its longevity. It was helpful that you suggest using at least a foot of crushed stone as backfill when constructing the wall. Is this something I can count on being done if I leave the job to a contractor that specializes in stormwater drainage?