Retaining walls help prevent soil from becoming displaced (more on that here). They can be used to create flat areas in a sloping yard, to prevent soil from becoming part of the run-off during the rainy season, and as part of the overall aesthetic of your yard. Many retaining walls can be installed by a moderately handy homeowner, but going this route has some pros and cons. Because putting in a retaining wall is a relatively complex, time-consuming project, be sure to put some careful thought into what the best choice is for you.
Advantages and Disadvantages of Professional Installation
Professional installation has some important things going for it:
- Experienced professionals
- Speed of installation (usually)
- Access to high-quality materials
- Knowledge of soil mechanics
- Knowledge of relevant building codes
Also, if you choose the right builder, you can control the design direction of the retaining wall.
Of course, a professional install is not always going to be speedier than a DIY job. However, having a professional do the same job that you were going to usually reduces time spent on the project considerably. If you hire a professional in order to use a more complex design, the time savings may be less or absent entirely.
The main disadvantage of a professional installation is cost. Labor costs will be a large percentage of the total price of having a retaining wall installed. Depending on the materials used, you may wind up paying mostly for a professional’s time. Of course, you are also paying for not only labor but also expertise.
Advantages and Disadvantages of DIY Installation
People decide to build their own retaining walls for a number of reasons:
- Lower cost (sometimes)
- Ability to completely control the design (although you do get this with some professionals)
- Fun hobby project
The major disadvantage of a DIY retaining wall is complexity. Choosing the right materials, proper placement, and type of drainage can be difficult for novice builders. The advantages and disadvantages of certain materials may not be immediately apparent. Some materials require more expertise to work with, such as poured concrete or timber.
Starting on a DIY Retaining Wall Project
If you do decide to go the DIY route, or even if you are undecided, your first step should be researching the process. Look at types of retaining walls and consider what you would like your retaining wall to do. Learn about the basic installation process for the various options. Once you have this background knowledge, you will be better prepared to make a decision about whether to hire a professional or not.
For intrepid DIY homeowners who choose to forge ahead, the next step is to look for any important details you may be missing. For example, consider whether the wall is high enough that you might need a building permit, or if any wall at all requires permission from your homeowners’ association. Consider where the water will drain, and whether your neighbors will appreciate it. Draw up some preliminary plans and ask a handy friend or acquaintance to look them over for any glaring errors.
If you follow some basic rules in order to create your preliminary design, the resulting wall will be much more effective and long-lasting:
- The wall should stair-step or lean inward
- You must account for and create proper drainage
- Compaction of the soil is an important and sometimes-neglected step
- The bottom of the wall should be buried to a depth of one-tenth of the total height of the wall
How much does it cost to DIY a retaining wall?
The main factors that affect the price of a DIY retaining wall are the materials used, transportation for those materials, and equipment rental or purchase. The materials cost is usually by far the highest:
- Timber: $10-$25 per square foot
- Natural stone: $8-$25 per square foot
- Stone veneer: $11-$15 per square foot
- Brick: $15-$25 per square foot
- Poured concrete: $20-$25 per square foot (not recommended as a DIY project, we can help you instead!)
Having large or heavy materials delivered to you can significantly increase their cost, so do your research if you want to build a boulder wall or one made out of large timbers. Most people will need to rent a plate compactor, which costs about $85 a day from a large home appliance store. Retaining walls also need gravel or crushed stone (about $30-$65 per ton), drain materials (varies), and waterproof backing (varies).
How long does it take?
The answer to this depends on a lot of factors:
- Your skill level
- Type of wall
- Length of wall
- Unexpected delays
Obviously, there is no planning ahead for unexpected delays, and weather can be almost as unpredictable, unfortunately. One estimate is to expect to spend about 20 man-hours for every 10-15 feet of low wall. However, this is widely variable.
Materials you’ll need (besides the main wall material itself)
No matter what kind of wall you choose to build, there are some additional materials that you will need:
- Gravel or crushed stone
- Landscaping fabric or waterproof backing
- Drainage piping (most walls)
- Extra soil
You will need enough gravel to fill six inches below the wall and 1-2 feet behind the wall. You may want to use landscape fabric or waterproof backing. Waterproof backing goes directly between the wall and the gravel. If you are using landscaping fabric, it is placed between the gravel and the soil to avoid clogging the gravel’s ability to drain.
Most walls will require a drainage system, which is usually made of perforated PVC pipe set in the gravel. Because you will be compacting the soil around the wall, you will probably need extra dirt, as well. This may come from another place in your yard, or be purchased separately.
Tools you’ll need to build a retaining wall
It depends a little on what materials you are building with. If you are building with wooden planks, you may need a saw, for example, that you would not need if you are building with stone. However, there are some basics that most people will need:
- Round-pointed shovel
- Square-edged shovel
- Plate compactor
- Rake (optional)
- Pick (depends on soil)
- Tape measure
A real tamper (also known as a plate compactor) is necessary for compacting the soil around the wall. A level keeps things even, and a hammer may be necessary if you need to drive stakes into the ground. A rake is useful for smoothing out gravel, but not required. If you have very hard soil, you may need a pick to get your trench started.
Design rules of thumb
A retaining wall should slope backward (into the side of the hill) 1 inch for every 12 inches of height. A straight wall would soon be pushed outward by the pressure of the soil behind it, so this is an important feature of a functional wall. It should not be built directly on the ground – most walls are buried 6 to 12 inches into the ground.
Basic steps for building a retaining wall
- Come up with a design plan. This should include, at a minimum, the height, length and location of the wall, the types of materials needed, and the required tools.
- Dig a trench where the base of the wall will be. This should be at least six inches deep, or at least one-tenth the height of the wall, whichever is deeper. Also clear out the vertical space 1-2 feet behind where the wall will be, if necessary.
- Add a layer of gravel to the trench and tamp it down. Lay landscaping fabric under the gravel, or waterproof backing over it. Place the first level of the wall in the trench and fill gravel in behind it. Add the perforated pipe to the gravel at the base of the wall and cover it with another layer.
- Tamp down the dirt in front of the wall, the gravel behind the wall, and the dirt behind the gravel with the plate compactor.
- Add another level to the wall. With each level of the wall, you should add gravel and tamp it down with the compactor. Tamp down the dirt behind the gravel as well. Do not wait to do it all at the end.
- Step each level of the wall slightly back. The wall should slope into the hillside at approximately 1 inch for every 12 inches of height. So, the top of a 3-foot wall should be 3 inches farther back into the hillside than the base.
- Finish the wall by filling in about 6 inches of lightly compacted topsoil over the gravel on the rear side of the fence.
Are there any building codes I need to watch out for?
In most areas, retaining walls of 4 feet or less do not require a permit. However, cities and counties are free to make their own rules and regulations, so it is a good idea to check with your local building authorities. It is worth noting that some cities allowing walls up to 4 feet in height are referring to the exposed height of the wall, while others are referring to the total height of the wall (including buried portions).
Make sure to check with your local utility company to make sure that there are no pipes where you are planning on digging.
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Choosing the Right Professional
If you decide that installing a retaining wall is not right for you, there are plenty of professionals out there who can do it for you. Choose one who has ample experience putting in retaining walls, and who will discuss the pros and cons of several options with you. If you already have a clear vision of what you want the wall to look like, discuss it with your builder and they can usually incorporate those elements into their design. Remember to also discuss logistics, such as how long the wall will take to install, when the builders can start, and what the entire project will cost.
The Bottom Line
Whether to hire someone to install your retaining wall or do it yourself is a matter of personal preference. If putting it up would be a chore and you can afford to hire someone, the answer is clear-cut. For most people, weighing the pros and cons will be required in order to determine whether you plan to forge ahead with a DIY project or pick up the phone and call a professional.