Retaining walls are a necessity in the mountains, where little flat land exists. Two of the main types of retaining walls are made of wood or cement blocks. Both materials have their pros and cons, so which one would be best for your landscape?
The first question to ask is whether or not the wall will be load bearing. If you plan on building anything above the wall, extra parking, a house, a deck, etc., then the wall is load bearing and block or concrete are the best way to go. Block walls are built to hold much more weight and are less likely to fail when built correctly.
If your wall will not be holding up any structures, a wood wall is the faster and cheaper option. At least initially. Block walls out live wood walls by decades.
For example, this retaining wall needs replacing mostly because of water damage. The rail road ties are worn and rotted from sitting in wet soil. Water has also pushed dirt between ties, where weeds have taken root and begun to expand the cracks. And while this wall isn’t technically load bearing, there is still a porch above it that depends on the ground to stay put.
Rail road ties are often the preferred over regularly treated lumber for wood retaining walls because they last longer. Even wood that is especially treated to resist water damage won’t last as long as rail road ties. The reason for this is because when the ties were originally made, the chemicals used to preserve them weren’t picked for their friendliness to the environment. When the ties do eventually begin to break down, they leach petroleum into the ground that can find its way into the water table. This can be especially alarming for those of us who have wells.
Concrete blocks won’t rot or break down and are designed to hold much more weight. They also interlace perfectly to prevent dirt from squeezing between the block. However water can also be the demise of a concrete block wall, if there is no drainage system in place.
When it rains, all of our beautiful red dirt becomes squishy, sticky, heavy, red clay that can hold water for days on end. A retaining wall by itself gives the water no place to go but straight down, which is a slow process with clay. All this extra weight for extended amounts of time can cause even the most well built wall to crumble. That’s why it’s vital to install a drainage system behind the wall. Gravel and strategically placed pipes the water to flow down and out much faster.
As popular as treated wood or rail road ties may be, they aren’t always the best choice structurally or environmentally. Block walls can be built taller and will last much longer in any landscape.