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How to Build a Treated Wood Retaining Wall: Setting It Up
Select a spot where you’ll have a clear view of the entire project. It should be well away from the wall so it won’t be disturbed during construction. Drive the tripod tips into the ground with your foot until the table is fairly level.
Mount the scope on the table and snug up the nut that holds the scope down.
Rotate the scope until it’s directly over two of the four adjusting nuts and twist the nuts until the bubble is centered in the vial. Then rotate the scope 90 degrees so it’s over the other two adjusting nuts and level it again. Repeat the process until the bubble stays absolutely level as you rotate the scope.
How To Use It:
A builder’s level has to be absolutely level to give accurate readings. Check the vial frequently during the day to make sure it stays level. Sometimes the legs get bumped or stepped on. You’ll have a lot of work to redo if you’re unknowingly using a scope that’s not true.
Looking through the scope, you’ll see crosshairs that will tell you the exact height of whatever is being measured (see Photo 7) relative to a “benchmark,” or starting point. In this case, the benchmark is the first footing. Take a reading from the first footing with a tape measure—let’s say it’s 58 in. If the next stake is 56-1/2 in., it’s 1-1/2 in. too high. It’s easy to get confused. Just remember: If a stake reading is a larger number than the bench-mark, the stake is too low; if it’s a smaller number, it’s too high.
How To Figure Out The Cost
This 40-ft. long by 4-ft. tall wall has a total surface area of about 320 sq. ft., and the lumber cost less than $1,000. You’ll spend another couple of hundred dollars for backfill gravel and hardware. As mentioned earlier, we also spent $250 on a skid steer with an operator to save the days of labor it would take to dig out the side of the hill and backfill the wall by hand.
You can estimate the cost of your wall by multiplying the square footage of wall surface by $3.75. That’ll take care of the lumber and gravel, but you’ll still have to add skid-steer charges. They’ll vary depending on the size of the wall and how much excavators charge in your area. Four bucks a square foot is about as cheaply as you can hope to build any retaining wall (unless you hand-gather fieldstone). By contrast, a concrete modular retaining wall runs about $8.25 per square foot for materials.
Save Your Back: Hire A Skid Steer With An Operator
If you’re hardy and have lots of time on your hands, you could do all the excavating and backfilling by hand, but that’s a huge job, especially for this design. Because the stanchions extend into the hill 4 ft. behind the wall, it’s necessary to dig out 4 ft. behind the entire wall level with the footings. It took three separate sessions with the loader to dig out and backfill our double-tier wall. First we dug the lower level back 5 ft. behind the face of the wall, then installed the lower wall. Then, we filled in behind the lower wall and prepared the hill for the upper wall. After the upper wall was finished, we backfilled and graded the entire area surrounding the walls to get it ready for sod. A single-tier wall would require only two sessions with the loader.
After you backfill, the dirt will settle significantly. We filled the walls all the way to the top, and after a couple of weeks, the dirt had settled almost an entire foot. Then we leveled out the earth by hand and used wheelbarrows to fill the rest with high-quality topsoil for the plantings.
Backfill With a Vertical Layer of Gravel Using Plywood "Slip Forms"
Establishing good drainage with a layer of gravel is essential for a long-lasting wall. Because the gravel is porous, it drains
water and separates water-laden soil from the wall. If you don’t use the gravel and you live in a frosty climate, frozen soil can grab hold of the wall, lift it out of position, and permanently warp it.
The Walls Go Together Fast!
One person spent a rainy day in the garage building the 22 stanchions we needed for both walls. This wall doesn’t
take long to build. It took a total of only 12 hours for two people to install both walls over two days.
Install a pair of homemade “slip forms” (Photo 14), then shovel in a thin vertical layer of gravel between the wall and the backfill dirt. Build the slip form by cutting a 2-ft. x 3-1/2 ft. piece of plywood and nailing a 2-ft. length of 2x4 at each end to provide the space for the gravel. Cut in a couple of handholds near the top for easier lifting. Shovel about 1 ft. of dirt against the form, then shovel 1 ft. of gravel into the form. Slide the form up until the gravel is within 1 ft. of the top of the wall. You’ll end up with a hill of hand-shoveled dirt that traps the gravel against the wall. When you’re through, you’re ready to have the skid steer finish the backfill.
An Optional Finishing Touch
Cap the wall with a 2x8 for a finishing touch if you wish. The cap is strictly cosmetic and doesn’t add to the structural integrity of the wall. If you opt for it, span 12-ft. 2x8s over the posts and secure them to each post with 3-1/2 in. deck
screws.
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