How to: Timber Retaining Walls

Design the wall and build a base. Decide how high and how long it must be. Timber retaining walls can be only a foot or so high or very tall, depending on the slope. Start any wall by measuring the area with a tape measure and marking it with wood stakes and builder's twine; put that line at least a foot behind the planned back edge for the wall. Excavate a footing along that line, at least a foot deep and a foot wide. Taller walls will need a bigger footing; walls only a couple of timbers high can get by with less.

Fill the footing trench with gravel to within about 6 inches of the dirt surface and compact it tightly. For higher walls, lay a layer of landscape fabric down before adding gravel. Set the first row of timbers, using a level to make sure they are level and the marking string to make sure the line is straight. Adjust the depth of gravel to level the timber top. For a tall wall, drill holes in both ends of each bottom timber and drive sections of reinforcing bar into the ground with a small sledgehammer. Use long metal spikes instead of rebar on small landscape timbers.

Add courses of timbers, overlapping joints. Cut timbers with a reciprocal saw or chain saw to fit as needed. Drill through each timber, for taller walls, and drive rebar spikes in to secure the timbers; use spikes with smaller timbers. Add a "deadman" every 4 to 8 feet for walls more than 4 feet high. A deadman is a section of timber run back into the slope perpendicular to the wall; the length will vary with the height of the wall.

Backfill the finished wall. Backfill shorter or garden walls with dirt removed for the footing or topsoil brought in. Fill taller walls by starting with 4-6 inches of compacted gravel at the bottom and finish with dirt to near the top of the wall. Leave a slight gap at the top between the wall and the dirt surface.