Slopes can create big challenges when building landscaping projects. Many structures, including sheds, walkways, gazebos, and patios, require flat surfaces. Even garden planting areas are much more effective if they are situated in flat areas of the yard. Retaining walls offer a way to create flat space for such projects.
There are two ways a retaining wall can be used to create flat space. To create a flat area in front of the wall, the process involves cutting back, or notching into the slope, then building a retaining wall to hold back the remaining hillside behind the wall. This is often the method used where the slope is quite steep. Alternately, you can build the retaining wall, then fill in the space behind it. This method is often used on gentle slopes, where you want to interrupt the slope with a tier of flat garden or lawn.
Retaining walls can create useful space from areas you once thought were unusable. If built properly, your retaining wall can last for many decades.
Retaining walls have structural requirements unlike that of any other landscape wall. Some garden walls aim at providing simple privacy, marking property lines, or keeping pets and children safely inside. These can be built from cinderblocks or stacked stone—or they can be simple fences made from wood or vinyl. But a retaining wall must hold back the earth itself, which can exert thousands of pounds of force when saturated with water. The design of a retaining wall must anticipate those stresses. For this reason, the space behind a retaining wall is usually filled not with soil, but with a porous, drainage-promoting material such as gravel or sand. Tall retaining walls may even build in a drain pipe or other features to shed water and lessen the pressure on the wall.
Retaining walls can be built of many different materials, including wood timbers, bricks, or natural boulders. But for DIYers, retaining wall blocks made of concrete are the best solution. Heavy retaining wall blocks keep the soil at bay with their weight. (The blocks we used in our demonstration weigh 14 pounds each.) Some do-it-yourself retaining wall blocks weigh as much as 61 pounds. But it’s the blocks’ accumulated weight that really does the trick. Our example, a three-tier wall with 14-pound blocks, weighs close to 500 pounds for each 8-foot stretch.
Concrete retaining wall blocks are shaped in a way that creates a natural setback as the blocks are stacked. A lip on the back of each block creates a uniform setback as each course is added. This design causes the wall to angle slightly back into the slope, further improving its holding power.
Permits and Codes
In many communities, retaining walls are among those landscape structures that require a building permit. Retaining walls may fall under zoning restrictions that dictate proximity to property lines, maximum height, and other conditions. Consult your local permitting department for advice; not all communities require building permits for a retaining wall. In some communities, no permit is required if the retaining wall remains lower than 4 feet and is not located in an environmentally critical area.
Where permits are required, the retaining wall must be constructed using sound building practices and cannot damage or pose a direct or indirect risk to neighboring properties. For example, you’ll be restricted from cutting back into a slope and building a retaining wall if the structure could potentially undermine land that extends into your neighbor’s property or affects drainage patterns on their land.
Source: The Spruce