The homes that are carved out of hillsides typically have a steep backyard that only offers minimal space for planting. In order to maximize the plantable space, many homeowners have turned to Landscape Contractors to build retaining walls. The two types of retaining walls commonly used by Landscape Contractors are brick/mortar and segmental. Brick and mortar is held together with concrete while the segmental stones rely on gravity and backfilling to keep them in place. The retaining wall serves a dual purpose for homeowners-protecting the home from potential mud slides and offering more space for planting trees, shrubs and flowers.

Steep slopes are not the only application of residential retaining walls. Many homeowners have a sloping hillside in their yard. By building a retaining wall at the base of the slope and backfilling with soil, a homeowner can sometimes double the size of his yard.

To define the pathway leading to this home, a small retaining wall was built using Anchor Diamond blocks, which are available in straight face and beveled three-way face styles. They provide maximum design flexibility for straight or curved retaining walls and terraces up to 3-feet in height.

Walls that are built with the brick and mortar technique require a footing of concrete with at least 90% compaction. In Orange County, the Environmental Management Agency specifies that walls greater in length than 100 lineal feet should be designed by a registered Civil Engineer. According to ASTM standards, the mortar for the footing should be freshly prepared and uniformly mixed in the ratio by volume of one part cement, 1/3 part lime putty, and 1/3 part sand. The grout that is laid between the bricks can be mixed in ratio by volume of one part cement and 3 parts sand. This type of retaining wall tends to be labor intensive and requires more preparation time for mixing cement and brick laying.

Segmental Walls

Stackable retaining wall systems, like those manufactured by Pyzique, Versa-Lok, Unilock and Keystone, are designed for ease of installation and versatility. They don't require mortar because they rely on gravity and pressure for stability. The installation of a retaining wall for residential applications requires a proper foundation, backfill, adequate drainage and level courses. Even walls that exceed 3 feet are fairly uncomplicated to construct. Segmental walls add layers and levels to the earth creating a unique outdoor environment for residential projects.

Though residential retaining walls are relatively simple to build and improve the stability of the land, Landscape Contractors must contact the city's building and safety department before any construction begins. If the project is located in an area that has county jurisdiction then you should call the county environmental management agency to inquire about local codes that regulate the design and construction of retaining walls. Regulations vary from city to city so it is important that you check with the proper authorities before building commences. For example, many cities don't have requirements for constructed walls under 3 feet. The City of Los Angeles, on the other hand, is very restrictive and anything over 18 inches requires a permit and the services of a soil engineer.

The second characteristic of a retaining wall that cities commonly regulate is horizontal setback requirements from existing buildings and property lines. The setback requirement is defined as the horizontal distance from the property line to the face of the wall. Based on his experiences, Miller said that most cities have a 5 foot setback requirement which means that you can't build any closer than 5 feet to the property line. If the setback requirement is not feasible for the project, then you can go before the planning commission to apply for a variance (justification to go around the code).

Finally, if the wall is built in the middle of a steep slope, the depth at which you imbed the wall is critical. This type of retaining wall is used to extend the backyard by backfilling to create more flat land adjacent to the home. The code may require you to bury the wall 2 to 3 feet, which will increase the materials and labor costs.

In order to protect the wall against erosion and hydrostatic pressure, adequate drainage must be provided. Landscape Contractors commonly use the french drain or the rock and pipe technique for drainage. According to Miller, a common drain detail for retaining walls is a 4" perforated pipe surrounded by gravel and wrapped in a filter fabric. (For additional drainage options refer to the article on page 32) To prevent water from spilling over the top of the retaining wall during heavy rainfalls, cut a "v" ditch that will allow water to discharge at the end points of the wall.

As more and more of these hillside homes are built, homeowners will rely on the services Landscape Contractors to make the most of their backyard environments. LCM

The four foot high retaining wall (top) was built in a few days by a professional installer. The 16" x 32" Lock + Load stones provide an architectural feeling of massive stone work yet are light enough to place by hand. (Bottom photo) Keystone residential retaining wall.