A true master with experience installing many of retaining walls, here are the rules of thumb that my son advises:
- For most residential applications use 4x4 by 10-foot pressure treated lumber
- Use 8-inch spikes to nail the rows together -using a spike at least every 4-feet
- Use 3-4-foot lengths of 1/2 or 3/4-inch rebar to secure to bottom two rows of the retaining wall into the ground below. Place a rebar every 4- 6 feet. Drill 3/4 pilot holes through the timbers to hold the rebar.
- Avoid making a retaining wall higher that 6 or 7 rows high. If you have to go higher than this it is better to have two or more staggered retaining walls as shown in the second picture..
- Secure the second or third row (from the top) of the retaining wall in to the ground behind the wall with a 'T- bar made of a 6-foot length with a 3-foot cross piece (as shown in the top picture). Secure the cross piece the same way the lower rows of the retaining wall was with rebar.
- Interlace the rows of timbers to provide strength of the joint at corners. Nail a 8-inch spike at each corner.
- Place a length of drainage tile (pipe) at the bottom of the retaining wall and exit the pipe out side of the retaining wall so that any water behind the retaining wall is adequately drained.