Retaining walls can help homeowners gain more useable space in their yard, and do a fantastic job of retaining the soil behind them.
They may seem pretty simple to build, but there is a lot that goes into a retaining build that will make or break how structurally sound your wall is.
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Who needs a retaining wall?
Retaining walls are a structure that holds, or retains soil behind it, and are designed to restrain soil to a slope that it would not naturally keep.
Areas that retaining walls are used are areas where the landscape needs to be shaped severely, or when a homeowner would like to gain more useable space in their yard.
Retaining walls can also act as an aesthetically pleasing focal point to any yard.
Anyone looking to spruce up their space with a gorgeous center piece, wanting more space In their yard, or have a problem with soil retention can benefit from having a retaining wall installed on their property.
Materials used in a retaining wall build
Retaining walls come in a variety of materials that can be used to build wall systems. These include concrete blocks (Allan Block), poured concrete, treated timbers (Wood retaining walls), rocks and boulders.
All of these materials can retain soil, but some will have a shorter lifespan than others. The two main retaining wall materials that are most common are wood, and Allan block.
Wood retaining walls
Wood is a natural resource commodity and being such does not have a company behind it offering building advice, warranty work, or ANY resources.
Most pressure treated lumber is not rated for ground contact. Meaning it’s supposed to be off the ground, and never touching soil. It really isn’t suitable for a retaining wall.
Typically, you won’t find ground contact lumber at your local Home Depot.
Wood is less expensive than concrete, and will last approximately 20-30 years.
Allan Block retaining walls
Allan Block retaining wall blocks, are a manufactured concrete product where every block is identical, and engineered to last a lifetime or longer. There are hundreds of resources available covering all scenarios. Backed by Engineers, scientific research, and evidence.
Allan block retaining wall blocks are a larger initial investment and will last a lifetime.
Retaining walls built with either of these materials will fail much sooner than expected if they are not properly installed.
If you are going to be putting in a retaining wall, we recommend using Allan Block over wood.
Should I build my own retaining wall?
We take pride in our yard’s appearance, and spend countless hours mowing our lawn, trimming our hedges, and pulling weeds in our garden. It is important to us that we take care of our home, and we get a certain satisfaction from being able to tell our friends that we did the work all by ourselves.
While we understand having pride in our work, there are some things that really need to be left to experts.
While there is lots of information out there about how to build retaining walls, a lot of skill and knowledge is required to install a wall that is going to not only do its job, but last.
How Hard is it to build a retaining wall?
Most walls are not built correctly whether from contractors and/or homeowners cutting corners by not using enough material (gravel) or not following proper specifications ( digging the trench deep enough).
To build a structural retaining wall takes considerable effort, and skill.
To build a reinforced retaining wall that will last, it takes the proper hand tools, gas powered concrete saw, laser level for perfect accuracy, string lines for straight and true walls, and the combined construction experience to put all this together, and to address potential issues before they become a problem.
There is also a fitness requirement, ability to handle stress, and working in the elements. As well as a skill to run heavy equipment: Excavators, skid steers, dump trucks etc.
Installation Of a Retaining Wall
The retaining wall installation is one of the most important things when it comes to building a long-lasting retaining wall in your outdoor space.
Both Wood and Concrete Allan Block walls retain soil. This means that decade after decade they hold back hundreds of thousands of pounds of soil. The drier this soil is, the less water pressure and weight they have to hold back.
The Majority of Retaining Walls Fail Because Of A Lack Of A Proper Drainage System Behind The Wall.
A proper drainage system is composed of a minimum of 16” of clear draining gravel directly behind the wall.
Gravel is essential for the base of a retaining wall to provide a solid level foundation to build upon. It drains water away to eliminate soil erosion, decomposition of the wall material, and to remove the standing water (proper drainage) below the wall system to prevent frost heave in the winter time
Without proper equipment, such as an excavator to dig the soil, and machines to bring in the gravel, it really is not feasible for a homeowner to bring in enough gravel for behind the retaining wall.
One major aspect to keep in mind is where the gravel that you are using to backfill the wall is going to be stored. Do you have room on your driveway for the gravel to sit for weeks while you work on this project?
The gravel cannot be stored on your road, so where is it going to be stored?
Keep in mind that this large amount of gravel will need to be delivered to you, as a regular truck will not be able to handle the weight and amount that you will need for your retaining wall build.
Excavation Of a Retaining Wall
Excavating the wall to the proper depth really requires a machine. While some homeowners are determined enough to try to hand dig, the amount of soil that needs to be dug is not feasible to do by hand.
Not only that, but you need somewhere to store all of the soil that was dug up.
Soil expands by 1.3-1.4 times in volume when unearthed, and produces a lot (We mean a lot!) of soil to excavate, load, haul, and dispose of.
Things to think about with this step of a retaining wall build are:
- Where to store the unearthed soil
- How are you going to move the soil from your yard to a truck to dispose of it?
- How are you going to get the soil from a wheelbarrow into a truck?
- How many loads is it going to take you to dispose of this soil? (Unless you have a dump truck, you are going to need to hire one to get rid of all of that soil)
Other Details for A Retaining Wall Build
Both Wood retaining walls and Concrete walls need to be laser levelled for grade accuracy, and installed with a string line for straightness. This helps the retaining wall blocks be completely straight.
If this step gets missed, it will be fairly obvious because the wall will be uneven and appear to be wavy. This step should be done by someone who has the skill and patience to take their time, and do it properly.
WELL OVER HALF of all retaining walls are in a state of failure, built unlevel, crooked, have gaps between the Ties/Blocks that open up more every year
What Happens with Allan Block Walls When They Are Not Installed Properly?
- Visually distracting if crooked or unlevel
- Will overturn if significant weight surcharge on top of the wall is not part of design
- Will show signs of movement between blocks or will overturn if water is not allowed to drain from behind the wall (No proper drainage system, like gravel)
Poorly Installed Wood Retaining Walls
- Visually distracting if crooked or unlevel
- Will show signs of separation and localized pushout/blowout if load behind exceed retaining strength
- Water left unaddressed will dramatically shorten a wood retaining walls life by rotting out the lower sections of the wall
What happens when a retaining wall is not built correctly?
Retaining walls that are not built correctly have varying levels of failure, from minor separation between the blocks, to catastrophic failure where large portions of the wall fall over.
Anything outside of Allan Blocks allowable movement for a flexible structure is a failure
Poor retaining wall design, installation method, or any other cost saving method will result in failure on some level.
Retaining walls are a big investment when built to best practices. Not only should they do their job of holding back hundreds of thousands of pounds of force (retained soil), they should be straight, true, and an aesthetically pleasing center piece in your outdoor space and landscaping backdrop.
Retaining walls are a large investment when they are built to Allan Blocks specifications, and are at least double the cost when they are not.
If a retaining wall is not built properly, it will cost more in the end when you have to tear your failing wall down, dispose of the materials, and re do your wall with new materials.
Oftentimes homeowners have given it their all, used up a summer of holidays, stressed themselves, and each other, spent valuable money they couldn’t afford to waste, and then had to call for help.
So, should I build my retaining wall myself?
In most cases, a retaining wall should not be a DIY for an ambitious homeowner, and should be left to professionals.
When a retaining wall is professionally built homeowners can have peace of mind that their wall will last, and that it will do its job of retaining the soil, acting as a focal point, and allow them more useable yard space for a lifetime.