How to Build a Treated-Wood Retaining Wall
Wall design and materials
Wall step up
This system allows you to step up along the primary slope as well as up the slope.
You don’t have to be a master carpenter to build this retaining wall. If you’ve ever built your own deck, relax—you already have the tools and skills you need. This wall is easier and more forgiving than any deck design. We’ll demonstrate the assembly, layout, backfilling and anchoring techniques that will make you comfortable tackling this project yourself.
This wall is unusual in that it doesn’t rely on dead weight or deep pilings to keep from caving in or shifting. Instead, it gets its soundness from the inherent strength of a rigid triangle assembly and the dirt that’s piled behind it. The very earth that’s the enemy of most retaining walls actually works with this design to give it strength. You don’t have to dig the wall in. You bury it in place!
The stanchions (post assemblies; see Photo 6 and Fig. A) have two short boards underneath the post to prevent settling. The headers, footers, braces and shelves anchor the stanchions deep into the side of the hill to keep the wall from tipping out or sliding away from the slope. A special steel strap (Photo 2) ties the 45-degree brace to the top of the posts to keep everything straight up and down.
Your walls can be as long as you want, but limit the height to 4 ft. Add more terraces as needed to retain higher slopes, stepping them back about 4 ft. If upper tiers will rest on earth that’s been disturbed from building a lower wall, you might have to wait as long as six months for the soil to settle naturally, especially in dry weather. Hasten the process by soaking the backfill (the fresh dirt behind the lower wall) with a sprinkler a few hours a day for a few days, and then allow a couple of extra days for the soil to dry out before starting higher tiers.
Every slope is different, so plan to establish a level base, then step it up or down as needed to handle hills that slope sideways. We stepped our wall in 5-1/2 in. increments so the 2×6 wall planks would continue to neatly stack at these transitions (Photo 10). To handle the transition between tiers, install bulkhead planks (Photo 15) between the upper and lower posts. First you have to make the lower and upper stanchions line up exactly. Use a carpenter’s square or a 4-ft. square to extend a straightedge to line up the first upper stanchion with the first lower stanchion.
We built the exposed surfaces of this wall with brown pressure treated lumber and below-grade members with less expensive green treated lumber. We chose the brown simply for its looks. If your lumberyard doesn’t carry brown, use green for all the parts and stain any exposed wood after the wall is up. Both the green and the brown wood used in this wall are rated for “ground contact” (not for below grade or foundation use). However, this wall will easily last a few decades—especially if you brush or dip the cut board ends with wood preservative (Photo 4). If you want your wall to be around for a century, use foundation-grade treated wood. But you may have to do a little detective work to find a supplier. Get out the Yellow Pages and start calling lumberyards. Most lumberyards will special-order it and charge more for the upgrade.
Special Tool #1: Skid Steer Loader
When you get into big retaining walls, you have to move a lot of dirt. It’s tempting to rent your own skid steer and do the excavating yourself. Don’t waste your time and money! We rented one and spent seven hours doing what a professional could have done in an hour and a half at a much lower cost. Hire the pro.
Special Tool #2: Builder’s Level
A good-looking retaining wall depends on level footings, and the best way to establish level over long distances is with a builder’s level. If you’re building a wall with only a couple of 4-ft. sections, you can get away with using a 4-ft. level, but for a longer wall, rent a builder’s level.
How to set 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 benchmark, the stake is too low; if it’s a smaller number, it’s too high.
Excavate and assemble the posts
Assemble the posts
Build a 90-degree assembly jig from 2x4s (shown in blue) to keep the stanchions square while you nail. Screw the jig to a sheet of plywood. Short 2×6 blocks hold the header 1-1/2 in. off the table. To assemble the post, center the 2×4 in the middle of the first 2×6 and nail it with 3-in. galvanized nails, keeping the top ends flush. Nail the header onto the bottom of the vertical 2×6 (flush with the 2×4) with two 3-in. nails at two opposite corners.
How to Build a Concrete Retaining Wall
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