A retaining wall is a practical outdoor feature that can help keep your yard in top form, but it’s often overlooked—or misunderstood. In its most basic form, it’s a structure that holds soil in place on a slope, and it’s built of modest materials, such as concrete, treated timber, or boulders.
But this is not a hardscaping project to be taken lightly. If not thoroughly planned or properly executed, retaining walls can be a disaster waiting to happen. Any mistakes could cause them to crack—or, gulp collapse—entirely.
“We estimate the average cost to build a retaining wall is around $5,000, so mistakes don’t come cheap,” says Dan DiClerico, a home expert at HomeAdvisor.
Nathan Outlaw, president of Onvico, a construction company in Thomasville, GA, says the biggest mistake that homeowners make is thinking that DIYing a retaining wall is a good idea. Spoiler alert: It’s usually not! “The best thing a homeowner can do is hire a structural engineer to design the wall so it can be built properly and there is some liability shift if it has issues,” he says.
However, if you’re confident in your skills to tackle this project, these are the mistakes you should avoid when building a retaining wall.
1. Choosing the wrong material
The good news is that retaining walls can be built with a variety of materials. However, that’s also the bad news if you make the wrong choice. Cinder blocks, poured concrete, wood, and rubble stone are some of the most commonly used options. But you must choose the right material for the climate you live in. For example, if you live in a moist or rainy area and use wood for your wall, termites and wood rot will reduce the wall’s lifespan. “Poured concrete, meanwhile, will be susceptible to cracking in climates with severe temperature swings,” DiClerico says.
2. Failing to provide adequate drainage
Did you know that neglecting to address water issues is the No. 1 cause of retaining wall problems? Joe Raboine, director of residential hardscapes at Belgard, says the most critical detail to ensure is that the wall drains properly, since both the surface water and groundwater can build up behind it.
“Water that pools on or behind your retaining wall can weaken it, particularly if it freezes and thaws,” says Joe Palumbo, president of Lakeshore Guys in Forest Lake, MN. “Pooling water can also erode or weaken the soil around the retaining wall.”
To provide drainage, Raboine says you can install a layer of clear backfill gravel and a perforated drain pipe.
3. Putting too much weight behind the wall
The higher your wall, the more weight it will usually have to withstand, and many states will require you to get a building permit and the services of an engineer if the wall is taller than 4 feet. “But even shorter walls could start to lean if they’re not sufficiently reinforced,” DiClerico warns. “This usually involves extending the footing, the reinforced concrete at the base of the wall that serves as the main support.” You might also need to install anchors or tiebacks for added support.
4. Tackling too much wall on your own
When DIYing a retaining wall, you need to realistically evaluate your abilities. “If it’s a very simple structure, say creating a raised, foot-high border in the yard out of reclaimed railroad tiles, that’s doable,” DiClerico says. But if it gets any more complicated than that, he recommends punting to the professionals. “We hear too many stories of pros getting called in to clean up the work of overly ambitious DIYers.” While the average repair cost is in the $600 range, depending on your mistake, DiClerico says the repairs could be thousands of dollars. Bummer.
5. Not doing maintenance
A retaining wall is not a “set it and forget it” project; it’s a structure you’ll need to inspect regularly. “Check for low spots behind the wall where soil may have settled,” DiClerico says. “They’ll need to be back-filled to prevent water from pooling and putting extra pressure on the structure.” And if you have any weeds, he says you’ll need to pull them out, since over time, their roots can compromise the wall. “Finally, be on the lookout for bulging on the wall or cracking—sure signs of imminent failure.”