Far too many retaining wall projects start with this simple step: homeowners see a clearance sale on retaining wall blocks, make an educated guess how many they need, and have the big box store deliver them. Once the pallets of block are stacked in the yard, they set aside a weekend or two, recruit some friends or family, and undertake a construction project.
We can easily understand “do-it-yourself” energy (we call it “the energy of the innocent”) because we’ve gotten over our heads in home improvement projects many times when we should have reached out for expert assistance. By the time the project is finally finished, we’ve made enough mistakes to learn how to do it right the next time. As we’re fond of saying, “anything worth doing is worth doing twice”.
Building decorative garden walls are very satisfying and rewarding, as well as being good exercise. When the purpose of the wall is more functional, it’s important to add an engineering step before starting the project. Retaining walls for purposes like holding back hills, supporting paving or buildings, and controlling runoff are serious projects with long-term consequences, so “learning by doing” isn’t always a good idea.
As a certified hardscape contractor, we often get called after the fact when structural retaining walls fail for one reason or another. This is never a pleasant experience for us or the homeowner. It’s vastly more expensive and time-consuming to fix a poorly-installed retaining wall that to install it in the first place. Usually, the cause of the wall failure is designed-in and the only solution is to remove it and start over.
In previous columns, we’ve offered retaining wall tips. Here’s a brief summary of the basic principles we’ve already talked about:
Hardscapes should never be built on fill, or on the ground that stays wet because of improper drainage. The center of gravity of a retaining wall should be BEHIND the wall foundation or footer. The taller the wall, the more it should start below ground. The heavier the wall, the more substantial the footer needs to be. There needs to be a way for water to freely escape from the footer trench, and from behind the wall, by gravity. Backfill behind the wall should be cleanly crushed (not round) stone.
Walls should be tied back into the hill so that the weight of the backfill prevents the wall from moving. Geotextiles are a typical method; there should be a layer of “geogrid” back into the hill every two courses on taller walls. Water runoff behind the wall should never be allowed to run into the backfill behind the wall. Curved walls, or walls with multiple corners, are vastly stronger than long straight walls.
Understanding these basics is a good start, but there are many more tips and tricks that come with training and experience. Every wall situation is different, and there are many different types of segmental wall systems, each with cost-benefit tradeoffs. We want you to succeed with every home improvement project you dream about. It’s important to know your own limitations before you begin.
Steve Boehme is a landscape designer/installer specializing in landscape “makeovers”. “Let’s Grow” is published weekly; column archives are online at www.goodseedfarm.com. For more information call GoodSeed Farm Landscapes at (937) 587-7021.