Wood Retaining Wall

Here's one way to tame a slope.

Check with your community's building department before setting out to build a retaining wall. Many codes require a permit for any structure that holds back what amounts to thousands of pounds of earth, and most limit the height of an amateur-built retaining wall to 3 feet. If your slope needs a higher wall or requires extensive grading, call in a masonry or landscape contractor -- or terrace the slope with two or more lower retaining walls.

Water is a retaining wall's worst enemy. Without proper drainage, water soon will buckle any structure you put up.

Come winter, alternating freeze-thaw cycles also can wreak havoc on a retaining wall. That's why it's important to drill weep holes or leave gaps between timber ends (see Step 4).

What You Need:

  • Pressure-treated 8x8 fir timbers (construction-heart redwood or cedar timbers are other good options, but avoid railroad ties; these are treated with creosote, which is harmful to some plants and makes the ties messy to work with)
  • Shovel
  • Level
  • Metal mallet or hammer
  • Chain saw and safety goggles
  • Heavy-duty drill with an extension bit (small drills burn out on long holes like these)
  • 3/4-inch rerod
  • Measuring tape

Instructions:

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Steps 1 and 2

1. Lay the first course. Cut a beveled trench into the slope, wet the trench, and tamp well. Set the first timber into place and level it. This course will be completely buried in the ground. We planned our wall to turn a corner; the same techniques apply to a straight wall.

2. Build up. Set a second timber on top of the first and bore a hole through the two timbers. Drive 3/4-inch rerod through the holes and into the ground.

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Steps 3 and 4

3. Stagger joints. Continue to place the timbers, staggering joints from one course to the next. Drill holes and use rerod to pin each timber to the one below on each side of every joint. When needed, cut timbers with a sharp chain saw; wear goggles to protect your eyes from flying chips.

4. Finish. Backfill as necessary. For drainage, drill weep holes every 4 feet along the wall's length. One row of holes about a foot above ground is fine. Instead of drilling holes, you also can provide drainage by leaving 1-inch gaps between ends of timbers.

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