Yet retaining walls that use masonry retaining wall blocks or those made from thick timbers can be difficult to build because of the overly heavy materials. As long as the height of the retained soil stays fairly low, you can build another type of wood retaining wall that uses lighter weight dimensional pressure-treated lumber.
Basics of Low Wood Retaining Walls
A low wood retaining wall does not need unwieldy tie-backs dug back into the slope, like many of the four-by-four timber retaining walls. Nor does this wall rely on sheer weight, plus a slight tilt, to hold back the slope, as do masonry walls. Instead, post holes are dug in the same way as you would dig holes for fence posts. Pressure-treated boards are then nailed across the backs of the posts, much like boards on a fence.
Safety Considerations
The wall and the soil behind it must remain low. Heights over 24 to 30 inches will result in too much pressure against the back of the wall, and the wall may eventually bend over and fail. Check with your local permitting office for information about recommended retaining wall dimensions.
Project Metrics
Working Time: 4 to 6 hoursTotal Time: 1 to 2 daysSkill Level: IntermediateMaterial Cost: $200 to $400
What You Will Need
Equipment/Tools
Post hole auger or manual post hole digger Hammer Shovel Power miter saw or circular saw Bubble level Laser level Measuring tape
Materials
(4) two-by-six pressure-treated lumber boards, each 8 feet long(6) two-by-eight pressure-treated lumber boards, each 8 feet long(2) two-by-six pressure-treated lumber boards, each 8 feet long(8) bags of 50-pound fast-setting concrete mix(8) 0.8-cubic-foot bags of 7/8-inch drainage rock(2) wood stakesScrap two-by-foursOrdinary twine or yellow braided nylon mason line16d hot-dipped galvanized nailsWood preservative
Instructions
This project will produce a straight, 16-foot long, wood retaining wall that is 24 inches high. The construction method used is suitable only for low walls of a maximum of 30 inches. Taller walls require a different type of structure. For durability, use only pressure-treated lumber rated for ground contact. So, you will be digging down 24 inches to account for the depth of the post, plus another 4 inches for a bed of landscape gravel. The hole for the four-by-four posts should be about 12 inches in diameter. Remove one stake at a time, then dig a hole with a post hole auger or manual digger (clamshell digger) at each stake point. With your tape measure, make sure that each hole is 28 inches deep. Install a final row of boards along the bottom, using two-by-six boards. The bottom edge of this row will be about 2 inches below ground level. It’s vital to back-fill with gravel and not with soil or even a combination of soil and gravel. If soil is used as a back-fill, it will become water-logged and excessively heavy, potentially collapsing the retaining wall.
