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PROJECTS ONLINE: BUILDING A TIMBER RETAINING WALL

Project Difficulty: Moderate
Estimated Project Time: 2 days

 
 
Tools and Materials:

8x8 pressure-treated landscape timbers
Measuring tape
Pencil and paper
Wood stakes
Shovel
Gravel
Tamper
Safety goggles
Work gloves
Dust mask
Spirit level
Circular saw
Power drill and 3/4" spade bit (or rent a heavy-duty drill and bit with extensions)
#6 (3/4") rebar
Reciprocating saw with metal-cutting blade
Sledgehammer
12-inch-long galvanized spikes
Perforated pipe

Shims
Dirt

 
       

Retaining walls keep soil from eroding down a slope. They can also transform a hilly backyard into a series of terraces for lawns, planting beds, or patio areas. On flat sites, low retaining walls can create raised planting beds or borders, adding a sense of visual depth to an otherwise uninteresting landscape. You can make retaining walls from a variety of materials: stone, pressure-treated lumber, brick, and concrete blocks. No matter what wall you intend to build, however, first check your local building codes for specific requirements.

A low timber retaining wall set on a relatively flat site, as shown here, is simple to build and requires little or no experience. This design works for walls up to 3 feet tall. The wall is supported by a gravel foundation. Drainage of groundwater is provided through the use of perforated pipe set behind the base of the wall as well as by the gaps between the ends of the timbers within the wall. The courses of timbers are secured with spikes and lengths of rebar.

Make a scale drawing of the wall and use it to determine the materials and the amount and lengths of lumber you will need. Also use the drawing to track the location of the rebar, joints, and "deadmen" (timbers placed perpendicular to the wall to provide additional support). Stagger the position of the joints between timbers so that they don't align vertically.

 

 
 
1 . Prepare the Site
Drive wood stakes into the ground marking the position of the wall. Using the stakes as a guide, dig a trench about 16 inches wide and to the depth required by local codes (some require to dig below the frostline especially in cold climates). Fill the trench with firmly tamped gravel.

2 . Cut the Timbers

Using a circular saw and wearing a dust mask, safety goggles, and work gloves, cut the 8x8 pressure-treated landscape timbers as needed to fit the wall (Fig. 1). Use your scale drawing of the wall as a guide.

3 . Drill Holes in First Course of Timbers

Using a power drill and a spade bit the same size as the rebar, drill holes in the first course of timbers, positioning them about every 4 feet (Fig. 2). You might want to rent a heavy-duty drill and a bit with extensions, especially for Step 7.

4 . Set the Courses

Lay the first course of timbers onto the gravel foundation, and use a sledgehammer to drive 2-foot lengths of rebar into the holes and ground until they are flush with the tops of the timbers (Fig. 3). Use a reciprocating saw with a metal-cutting blade to cut the rebar to size. Position perforated pipe, with its holes downward, behind the entire first course.

Lay the next course (and subsequent courses) of timbers on top as planned for in the scale drawing. For additional strength, spike the courses together using 12-inch galvanized spikes placed about 2 feet from each joint.

5 . Set Deadmen

To resist tipover, set a few timbers, called deadmen, perpendicular to the wall, and spike them in place. (Fig. 4)

6 . Level Each Course

As you build the wall, check each course for level, particularly where long timbers are cut short to fit around the deadmen (Fig. 5). If necessary, insert shims to make the timbers level.

7 . Finish the Wall

Once all the courses are in place, drill long holes for the rebar. Place the holes about 8 to 10 inches on either side of the joints in the top of the wall and continue down until they exit the bottom timber. Make sure not to drill into the rebar holding the first course to the ground or the spikes holding the timber ends together. Drill a hole through each deadman and into the ground as well. Use a heavy-duty drill with extensions.

Drive 24-inch lengths of rebar through the deadmen and into the ground. Cut the rest of the pins so that they're 2 feet longer than the wall is high. Then using a sledgehammer, drive the pins through the timbers and into the ground.

Backfill behind the wall using dirt and gravel and burying the perforated pipe and the perpendicular timbers (the deadmen). (Fig. 6)

 
 
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