By definition, a retaining wall is a structure that is used for supporting the soil mass laterally, so that the soil on different sides of the wall is retained at different levels.
Retaining walls are, thus, used to bound two soils between two different terrain elevations in situations where possessing slopes would be undesirable. Such situations include building a basement, but the more common instances when we use retaining walls are gardening and landscaping.
Of course, although it is very easy to assume that a retaining wall is simply a wall that was built to hold a certain type of soil, things are not as simple as they seem. For instance, unlike normal walls that have lateral support at the top, retaining walls don’t. Normal walls are built to bear vertical loads while retaining walls are dealing with horizontal loads.
Obviously, this difference entails different engineering approaches. Unlike the situation when we want to simply separate an empty space, the presence of vertical load can be addressed with the use of gravity walls, piling walls, cantilever walls, and anchored walls.
However, in a huge number of situations (gardening) the vertical pressure is not that horrifying, so the ability of the wall to carry the bear of the load is mostly determined by the ability of the build material to deal with this situation.
Therefore, we will take a look at some of the most common build materials and see how well can they play the role of a retaining wall.
Table of Contents
- A. 8 Retaining Wall Designs (Diagrams)
- B. 10 Retaining Wall Materials
A. 8 Retaining Wall Designs (Diagrams)
Below is a series of diagrams showing how to to make strong retaining walls. We set out several structural approaches.
1. Anchored Wall
2. Cantilevered “L” Wall
3. Cantilever Wall
4. Counterfort Wall
5. Gravity Wall 1
6. Gravity Wall 2
7. Piling Wall
8. Achored Wall (Screw Design)
B. 10 Retaining Wall Materials
1. Concrete Blocks
Concrete blocks are a very modern and sophisticated material. Because it is artificially produced, concrete offers a lot of flexibility and variety to choose from. Also, in spite of the common belief that concrete blocks leave a very sterile impression, this material plays extraordinary well with the Spanish architectural style. Concrete walls are usually designed to be set on a compacted gravel base and remain strong even when you apply pressure.
- Durability – A concrete wall can often last up to a whole century.
- Variety – Concrete blocks come in different shapes and sizes and can be used to create curves.
- Ease of installation – Concrete block walls are usually much easier to install than some other, more labor-demanding block types.
- Low maintenance – You can clean the blocks only once per year.
- Eco-friendly – Concrete walls are non-toxic and they do not emit allergens or dangerous chemicals.
- Architectural demands – Concrete walls have to be carefully designed, so you should ask for a professional advice about the issues of drainage and effective support. Also, the lack of proper support may affect durability.
- Lack of height – Concrete block walls can be used only for walls that are no taller than four feet. So, if you, for instance, want to raise your rose beds to higher levels to protect them from deer, you will have to look for another material.
- Complicated to remove – If you ever decide to change the placement of the wall, you will have to undergo a lot of trouble to dismount it.
Concrete blocks usually have very balanced and uniform prices. Capstones usually cost approximately 95 cents apiece while the average cost of the block is 1-3$.
2. Stone veneer
Stone veneer is a protective material that can be used as a decorative covering for vertical walls and surfaces. That means that the veneer itself is a purely aesthetic element and it needs a solid core to even work as a wall (a role usually played by CMU blocks). However, it looks stunning (stone veneer simply oozes luxury) and brings enough of its own unique personality to earn a spot on the list.
- Durability – The natural stone is a powerhouse build material. Stone structures are capable of withstanding centuries of abuse, and your retaining wall (or at least its façade) will be capable as well. It will not fade, and it will not crack.
- Look – Natural stone has a very beautiful aesthetics and texture. Beautiful patterns, unique shapes or even the lichen growing on the rock are very hard to be emulated by other materials.
- Light weight – Although not amongst the lightest materials on the market, stone veneer is reasonably light. That makes building the wall much easier.
- Flexibility – The solid core can be built in literally any thickness or height.
- Cost – Unlike some other, manufactured materials, natural stone is not that affordable.
- The ease of installation – Installation of stone veneers usually involves the services of a professional contractor.
- Design problems – Matching all the individual pieces with existing architecture is not always easy.
- Solid core – Stone veneer is not a freestanding element, so you will have to double the work.
The price of stone veneer usually varies from $6 to $9 per square foot.
3. Poured Concrete
Poured, or how people like to call it cast in place concrete is a very popular architectural option produced by pouring the concrete directly into the forms on the site. Since it looks very clean-cut and sterile, poured concrete plays along the best with the modern-looking surrounding. The ability of the concrete to support the soil load depends on weather conditions and other elements.
- Strength – Since it features much bigger density than block walls, the walls built out of poured concrete are much stronger as a result.
- Variety – Concrete can be poured in any form you can think of. That gives you a lot of design options to choose from.
- Consistent look – The concrete may look sterile, but at least it looks consistent. You always know what you’ll get at the end.
- Flexibility – Poured concrete makes incorporating other architectural elements like, for instance, drainage systems very easy.
- Susceptible to crack – Concrete walls usually need some kind of structural support (e.g. steel rods). If they don’t, they may crack.
- Building requires a lot of skill – The forms you are going to pour concrete in must be immaculate and perfectly set up. The required skill makes it very difficult residential project.
- Moisture – When exposed to excessive amounts of water, concrete tends to become unacceptably damp. That may damage surface treatments such as paint.
- Vulnerability to chemical damage – Concrete can be easily damaged by a number of chemicals like chlorides, sulfates, and even distilled water.
Estimating the price of the poured concrete is not that easy because you have to take into account the costs of concrete forms, sub-base preparation, reinforcements, and finishing. However, we can say that, on average, the price per square foot varies between $3.25 and $5.25, or $93 per cubic yard.
Brick is one of the most popular building materials, and it is very easy to see the appeal. First, in contrast to concrete, and even stone, bricks feature a very warm and inviting look. They do a wonderful job complementing traditional homes and landscapes. But, the look can push some building material only so far. Bricks have a lot of other good things working for them as well.
- Low maintenance – Brick is a relatively low-maintenance building material. Also, it retains color rather well so you won’t have to bother with painting for too often.
- Eco-friendly – Bricks are made out of some of the most abundant and eco-friendliest materials in the world – shale, and clay. Also, bricks can be later repurposed for other landscaping projects like walking paths.
- Weather and fire resistance – Bricks are playing extremely well with the elements. They are not damaged by dampness, and they can withstand a lot of abuse caused by flying debris. Also, bricks are not combustible and don’t help the spread of fire.
- Durability – A solid, well-made brick is as durable as you can wish for. Nowhere near as durable as stone, but durable nevertheless.
- Price – Bricks befall into the upper price segment of outdoor building materials.
- Color limitations – Although they come in a range of different colors, compared to some other materials, bricks do not offer the same degree of variety.
- Heavy – Bricks are quite heavy material. You have to pay attention to make your retaining wall a solid foundation.
- The lack of flexibility – Changing the outer appearance is problematic, but nowhere near as problematic as replacing a damaged brick.
A brick with a selling price of $340 will cost you $1.96 per square foot. A brick costing $500 per thousand will require that you pay $2.88 per square foot.
Wood shares a lot of same qualities as bricks. Both these materials have been with us forever, they both lend the space they occupy a sense of nostalgia and warmth and they are both made out of widely accessible materials. However, when it comes to their building material properties, they couldn’t be further from each other.
- Natural look – Wooden walls have a tendency to blend into the landscape quite seamlessly.
- Cost – Wooden retaining walls are usually very cost effective.
- Ease of installation – Wooden retaining walls are very easy to install which makes them an ideal DIY landscaping project.
- Lightweight – Although reasonably durable, wood is a very lightweight material that is easy to dismantle, move around and repurpose.
- Limited lifespan– Out of all materials on the list, wood probably has the shortest lifespan. However, with the proper maintenance, you will be able to squeeze good 20 years of service out of it.
- Wood rots – With the proper treatment this unfortunate outcome can be postponed but not avoided. If you are living in an area that sees a lot of rain, you should probably skip this material.
- Strength – Although they can handle retaining walls under the height of four feet, wooden planks are not recommended for some more complex projects. They can protect your plants from the smaller breeds of rabbits, but they won’t cut it when it comes to bigger and agiler pests.
- Susceptible to termites – If you don’t pay enough attention these small pests can ruin your installation.
Wood retaining walls usually start $15 per square foot.
Boulder walls are, without any doubt, one of the oldest and the best lasting kinds of man-produced structures. Unlike quarried stone or manufactured modular blocks, boulders are widely available and ready to go even without any additional refining. At the same time, they retain most of the positive aspects of the furnished stones and can last you a century (at least). Stone boulders are a perfect fit for any kind of country, colonial, or English-style garden.
- Natural look – Boulders are a great match for any kind of rustic home or landscaping design.
- Ease of use – Boulder walls are extremely convenient to build. Some of the projects can be easily accomplished simply by stacking the boulders on top of each other. Building the wall doesn’t involve expensive equipment.
- Availability – Boulders of all colors and sizes are extremely easy to obtain and at a very affordable price.
- Durability – As we already mentioned, boulder constructions are in use since the beginning of humanity. Some of them are still alive and well. That should serve as an enough of a testament to boulders’ durability.
- Size – Boulders tend to be quite large. So, if you own a smaller yard, you should probably skip them – they will eat you a lot of space.
- The lack of flexibility – Boulders are what they are – there is very few interventions you can make on them. Therefore, they can be used for the most basic tasks (elevating a section of soil), but not so much for some of the more complex projects (controlling the water flow).
- Transportation – If the blocks are not locally available, transportation can burn you a lot of money.
- Height – Boulder walls can’t be built as high as concrete walls.
Due to their uneven size, transportation costs and a wide variety of available types determining the price of the boulders is not that easy. However, it is safe to say that they can be obtained in the price range between $100 and $600 per ton.
Gabion is a very old method of building the walls. The very name is derived from the Italian world gabbia which stand for cage. And that pretty much describes the gabion walls – they are simple cages made out of wire or steel rods and usually filled with rock or rubble. Although they had the widest application in the times of war (during the Civil War, gabion walls were built to protect the soldiers), their ability to play along with virtually any kind of recycled material (e.g. crushed concrete) earned them a very loyal following amongst the modern eco-aware audience.
- Heavy basis – Gabion walls will stay firmly in the position even in the case of the worst downpours you can imagine.
- Flexibility – The baskets and the very materials within them are very flexible and extremely easy to fit in any kind of backyard setup.
- Upgradability – Gabion walls are modular. Thar mean that each of their sections can be easily replaced or upgraded. Also, the gaps between rock or concrete pieces can be filled with vegetation and silt which should further reinforce the wall.
- Ease of use – Gabion walls can be built even with the slightest knowledge of masonry or architecture. The build times are very short and the transportation is extremely easy to handle.
- Visual appeal – Although they can play along with a wide variety of coastal and riverside homes, gabion walls are not that visually pleasing.
- Prone to rust – If you don’t put enough care into maintenance, wire baskets can easily rust away, and render the whole setup worthless.
- Vulnerable to water – Exposure to water can damage the basket and cause the corrosion of internal elements (depending on the elements).
A regular gabion wall usually costs $35 per cubic yard (and that would be a three-feet square cage).
Although they, at least on the first glance, look the same, wood and timber are not considered to be the same building material. Well, at least not quite. The word timber is used to describe any stage of wood after the tree has been cut. The so-called “finished” timber is the wood that’s been processed and cut in various sizes, but still column in nature. As we can see, that makes timber a very different building material from the planks we mentioned above. What these differences amount to?
- Affordability – Cheaper timber pieces are much more affordable than some other materials used for building block walls.
- Durable – Thick timber pieces are much heavier and more durable than wooden planks.
- Good-looking – Any kind of wood ought to bring a lot of old-school charm into your backyard and make a very strong impression on the observer.
- Easy to install – Timber retaining walls have a lot of structural integrity, even if you simply stack the pillars on top of each other and a nail them together.
- Wood rots – Although timber walls are said to last at least 15-20 years, many of them are not that lucky.
- Lack of flexibility – Timber pillars are very large and bulky. Making any kind of advanced design with such building blocks is not that easy. Of course, you can always cut timber into smaller pieces or combine the materials.
- Susceptible to termites – Again, much like any other piece of wood, timber is vulnerable to these pests as well.
The cost of installation of timber retaining walls varies from $16 to $19 per square foot.
9. Natural stone
In a sense, natural stone walls are very similar to boulder walls. The only obvious alteration is that natural stone pieces are much smaller. But, that makes all the difference in the world. Natural stone, therefore, retains all the good qualities of other types of stone (tradition, strength, durability), while allowing you much more design options than, for instance, boulder pieces.
- Look – Stone simply looks beautiful, and fits perfectly into any kind of traditional rustic setting. Because you are working with a lot of smaller building blocks you will have more freedom to experiment with different colors and textures.
- Flexibility – Natural stone can fit almost any situation that comes to your mind. Also, you don’t need any special connection or mortar to keep the construction together.
- Tradition – Natural stone is one of the oldest and the most reliable materials used for grade transitions.
- Durability – Much like any other stone construction, if made well, a natural stone can last you for ages.
- Price – Stone was always considered to be one of the more pristine, but also the most expensive building materials.
- Drainage – When it comes to natural stone, drainage can become a serious problem after just a couple of years.
- Heaviness – Setting up a stone wall is a very labor-intensive process.
- Building blocks diversity – Fitting too many different pieces together may prove to be a joy for some, but a chore for others.
Depending on the type of the stone you’ve chosen, a natural stone retaining wall will cost you $8 to $12 per square foot.
Limestone is a sedimentary rock, composed of skeletal fragments left over by the marine organisms (mostly corals and mollusks). Its primary materials are calcite and aragonite. Although that may probably make you think limestone is more fragile than traditional rock, you have to remember that some of the most long-lasting structures in the world like Taj Mahal and Great Pyramids of Giza were made out of this material. That doesn’t mean that limestone doesn’t have its unique set of advantages and disadvantages.
- Looks – Limestone boulders are usually yellow or gray and land a very timeless and classy feel to the space they occupy. If you are in favor of the look of the desert-bound structures of the times long gone, this is the material for you.
- Durability – Limestone is fireproof, wheatear-resistant, bug-resistant, and impact-resistant. As the time goes by it doesn’t lose any of its visual appeal.
- Maintenance – Limestone retaining walls are very easy to clean. All they require is a gentle brush.
- A variety of different types – Limestone offers a lot of different varieties to choose from. Sandblasted, split-faced, polished, rubbed, gray, silver and variegated are only some of the offers on the table.
- Susceptible to chemicals – While limestone can withstand pretty much anything Mother Nature can throw at it, it doesn’t bode so well with chemical solutions. The most common cause of weathering is rainwater high in carbon dioxide.
- Susceptible to staining – Due to its highly porous nature, limestone is very susceptible to watermarking and staining caused by other liquids.
As we already mentioned, there are a lot of different types of the limestone boulders around the market, so you can expect their price to vary a lot. But, as an example, the price of weathered limestone can go up to $515 per ton.
11. Segmental Retaining Walls
A segmental retaining wall is one that is constructed by identical pieces of pre-cast concrete that interlock and anchor into backfilled soil. These types of alternatives to retaining walls are most commonly used with geotextiles when the grade of a slope is greater than 45 degrees and a reinforced soil slope is not recommended. The installation of a segmental retaining wall is currently $5350.00.
- Segmental retaining walls provide the retention needed to keep slopes from caving, slumping or sliding.
- You can build retaining walls that are straight, curved, a combination of both as well as offering you the opportunity to add steps and corners.
- There is no need to install concrete footing as there is with wooden timber and natural rock walls.
- Segmental walls can be used to create additional patio space, widen patios and walkways.
- They come in a wide variety of colors, textures and sizes.
- Since the pieces interlock, rapid construction of your wall is possible.
- Higher and steeper walls are able to be constructed.
- The concrete used to create segmental walls is extremely durable and very low maintenance.
- The area where your segmental retaining wall is to be built must first be drained of excess rain water and ground water.
- Weepholes and drainage lines must be taken into account when building this type of wall.
- This type of wall requires more in-depth planning than the average person can handle because of design and drainage demands.
- To ensure that the geogrids are being properly constructed, and engineer should be consulted to ensure the safety and viability of the wall.
- If you ever decide to rearrange or remove your wall, it will be very difficult to do so.
Emily Taylor has a huge passion for gardening with the urge to know and control every little thing that happens inside her house. When she isn’t glued to her backyard or caring for the house, she spends time writing her blog Lovebackyard.com hoping to share her tips and stories to people who want to transform their house into a real paradise. You can reach her at [email protected] or on Twitter at @Emily_Taylor9.