Project of the Month: Modular Landscaping Walls

This month we feature Modular Landscaping Walls. In keeping with the trend of "do it yourself" markets, many construction material manufacturers and suppliers are making the art of installing short retaining walls more user friendly. Read further to clearly understand the benefits of a Modular Retaining Wall.

Today, a home owner can purchase modular blocks to build this same wall. Modular blocks are similar to a child's Lego toy set where small manageable blocks can be connected to create a structural, useable shape. Although many variations are available, modular blocks have a number of common characteristics. First, they all are small; one person can handle each block without special equipment. Second, the blocks have an interlocking system allowing them to be structurally stable up to a certain height. Pins, clips, recesses, protrusions and geometric shapes are all used to tie adjoining blocks. Third, since the blocks are pre-cast concrete, they can be obtained in various colors and finishes. Standard colors are typically red, tan and black. The finish can be rough, appearing to be worn, and natural or smooth for a clean appearance. Finally, the shape of each block is such that the wall can include curves and angles.

Each manufacturer of modular blocks has their own set of installation requirements. Prior to designing a wall, these requirements should be reviewed. There are, however, several design and installation procedures that should be followed regardless of block type.

Height
First, the designer should determine if the wall is to be landscape-oriented or structural. Most manufacturers of modular block indicate their products are stable up to 3 to 5 feet high. Walls taller than recommended have additional design and construction requirements.

Foundation
All modular walls require a foundation. For landscape purposes, most manufacturers suggest the first layer of block be set on a layer of granular material. Figure 2 is typical of the cross-section used in many product brochures distributed by modular block manufacturers.

Figure 2 Modular Landscape Wall

This detail shows a layer of compacted, crushed rock placed on compacted earth. This foundation must be wider than the first row of block. A crushed stone foundation will move vertically depending on the season, weather and moisture content of the soil. Since the blocks in a modular wall are not attached with mortar, the wall can move as the foundation fluctuates without permanent damage.

Drainage
As mentioned, a crushed rock foundation will fluctuate without causing permanent damage to the modular wall. Excessive movement, however, will damage the wall. To control excessive movements, the moisture content surrounding the foundation and wall must be controlled. A perforated pipe drainage system is required behind the wall, as shown in Figure 2. In addition, the terrain behind the wall is graded to drain any surface water away from around the wall. The ground in front of the wall is graded to keep water from ponding against the face.

A modular wall should be designed with the natural terrain in mid. Sharp angles and direction changes are not only complex to build, they add stress points to the wall that may cause failure. The designer should stake the alignment of the wall before beginning construction. Location of the ends should be placed so the wall will "grow" to a predetermined height and then return to ground level.

Do not forget to take advantage of the size and flexibility of modular blocks. Many walls have benches and flower beds incorporated into their design. These walls are used not only to adjust the terrain, they also enhance the owner's property. Properly placed, these walls are used for sitting, climbing, playing, and planting as well as landscaping.

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