The earth, as we know, is far from flat. Its surface is rife with hills and valleys, slopes and slides. So, rather than eliminate huge swaths of land for potential habitation, ancient man came up with a brilliant idea to build structures that resist the downward pressure of soil. Thus, one of the oldest hardscaping inventions of all time was born: the retaining wall.
Over the last few decades, though, the retaining wall has evolved past a thing of pure function, into an evocative focal point of modern landscape design.
Retaining walls are as common to the Georgia landscape as kudzu. The reason being: the central part of the state is one giant rollercoaster, thanks to the hills of the Piedmont Plateau. Add in the area's highly acidic, mineral rich soil and you've got a mini mudslide waiting to happen at every hard rain.
Here are the chief benefits of retaining walls:
- Prevents soil down-sloping, urban flooding, sink holes, and surface erosion
- Provides structural support for grade changes, thus evening the score, so to speak
- Protects waterways from fertilizers, petroleum, and pesticides leaching into sewers from soil
- Creates a dramatic, high-impact entrance to a home, thus increasing its curb appeal
- Frames different areas of a backyard into specific units
- Affords privacy from neighbors
- For small backyards built into steep hillsides, retaining walls carve out more livable space for entertaining, gardening, sports, and so on
Six Key Materials
What a retaining wall is built out of depends on its overall purpose and the owner's personal aesthetic. These are the top six materials used:
- Modular Concrete Blocks
Known as SRW's, or segmented retaining walls. These are high-quality, man-made, pre-cast concrete blocks. Recommended for gravity wall structures of four feet in height or below. The appeal of SRW's is broad:
- The interlocking, airtight joints make them one of the strongest and longest lasting materials, holding up to pressure for 50 years
- Unlimited variety of colors, shapes, and sizes to customize a specific vision
- Can be incorporated into designs that call for horizontal or vertical curves, corners, steps, and so on
- Quickly installed, no waiting for cement to dry
- Solid or pitted. A popular trend is to use hollow blocks and plant flowers, shrubs, or creepers in the open faces
- Textured to resemble natural stone. A popular trend is blue or gray castle wall blocks
- DIY-and budget-friendly
- Allow backfill soil to drain itself of water through the face joints
- Natural Stone
If the budget allows, it's hard to contest the beauty and grandeur of natural stone veneers. From bluestone to quartz, fieldstone to flagstone, the options are plenty. But while stone provides unmatched structural integrity, it also presents certain challenges:
- Natural stone is quarried, and must be shipped from its place of origin, a costly endeavor
- Installation is labor intensive, as each stone must be individually cut on site
- Only an expert stone mason can ensure proper moisture control during the stacking process
- High maintenance
A popular option for lower retaining walls, especially those encompassing gardens, is the boulder wall: large rocks are laid in a free-form, organic design
- Poured Concrete
A uniform concrete slab is poured. This option is popular for modern designs; those seeking clean, contemporary lines. Great for high walls. Also, concrete can be dyed any color, and molded into any desired shape.
Create the design of your choice, from classic running board to elaborate herringbone
This is the most common choice for D.I.Y.'ers due to its simple installation. Options include:
- Composite boards: Precut, prepackaged boards made of recycled plastic and natural wood fibers. Comes in hundreds of realistic grains. Popular for simple, modular gardens. Wont warp, rot, splinter or fade
- Landscaping timber or salvaged lumber: Cedar, redwood, juniper, Douglas fir, and so on. It’s highly recommended to buy this wood from a local salvage store, as the staff has already sorted, fumigated, and treated the wood worthy of reuse.
There are also chemical-free, responsibly sourced timber suppliers for eco-conscious buyers
- Railroad ties: Popular between 1950s and 1980s for their durability and affordability. But any baby boomer remembers that strange smell RR ties gave off in the heat of summer; that was toxic creosote burning off, making RR ties timber non-grata today.
While easy to install, wood retaining walls are subject to rot, warping, mildew and termites if not treated properly.
Derived from the Italian word gabbione, meaning "big cage." The earliest versions were made of woven willow wattle akin to giant wicker baskets, used for securing the banks of the Nile River 7000 years ago.
Today, gabions are made of sturdy, galvanized stainless steel. And over the last decade, they've made a huge comeback in the retaining wall industry, especially when space isn't an issue and environmental-friendliness is. Gabion cages are generally quite wide, and filled with any sort of recycled organic material: concrete blocks, broken bricks, timber, basalt rocks, and so on.
- Pros: They are highly sustainable, permeable, and self-draining. And new wire technology and coatings protect them from rusting
- Con: They are great hiding places for small critters
Note: Before starting any retaining wall project, check with your local building codes, home-owner's association, and call 811 to assess for underground utilities.
If you need a professional in the Atlanta area for all things concrete, give Concrete Solutions a call for a consultation.