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How to Build a Treated Wood Retaining Wall: A Lightweight but Rugged Alternative
This Unique Wall System is Self-Supporting
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.
Dealing With Side-Sloping Hills
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 2x6 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.
Use Brown-Treated Lumber for the Parts That Show
FIG. A Wall Assembly
Click image to enlarge.
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 (we used a brand called Cuprinol; see Photo 4). If you want your wall to be around for a century, use .60 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 about 30 percent more for the upgrade.
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