Retaining walls of wood (shown in cross section, right) are probably the least expensive and easiest to build. Because the wood contacts the soil directly, you’ll need a rot-resistant type such as redwood, cypress or pressure-treated wood rated for ground contact (the longest lasting of the three).
Most walls have posts made from 4-by-4s, 4-by-6s or landscape timber. They are set in a deep, concrete-lined hole to provide support. A perforated pipe behind the wall provides drainage.

Step-by-Step
This wall is 34½ inches above grade.
1. Dig and clear a level area.
2. Use stakes and mason’s lineto mark the locations of the wall and posts. The back of the wall should stand 12 inches from the bottom of the cut into the slope.
3. Dig postholes 42 inches deep on center and 3 feet 10 inches apart for the 4-by 4-inch posts. After aligning the postsadd 1 inch of soil or gravel to each hole around the bottom of each post, and fill with concrete. The top of the concrete should sit 2 inches above grade and should be rounded to help water drain away from the post.
4. Nail horizontal 2-by-6s to the soil side of the posts. Space 2-by-6s 1/8 inch apart to allow for expansion.
5. Use a handsaw to trim the post tops flush with the top board, then center a 2-by 8-inch cap over the posts and wall boards.
6. Install drainage behind the wall.

By the Book
Building codes for retaining walls vary. Check local code requirements before you begin.

Tools
4-foot mason’s level
combination square
mason’s line
posthole digger
hand or circular saw
shovel
wheelbarrow

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