How to Build a Pressure Treated Lumber Retaining Wall

Building a lumber retaining wall is a fantastic way to bring both form and function to your backyard landscape. In terms of difficulty this project rates on the more high side on the homeowner’s scale. They’ll be plenty of manual labor required to move wheelbarrows of material and heavy timbers. But if you’re up for the effort, they can be one of the most satisfying projects you can tackle.

To get started you’ll need the following tools and materials:

  • Square head shovel
  • Spade shovel
  • Hand tamper
  • Wheel Barrow
  • Impact Driver
  • 4 inch perforated drain pipe
  • ¾ inch stone
  • Landscaping Filter fabric
  • ½ inch 4 foot long rebar stakes
  • 6 x 8 inch pressure treated timber
  • 12 inch landscaping screws
  • 9/16 inch drill bit
  • 4 Foot Level & Torpedo level

Step 1 – Layout the Wall

 The first step is to make sure the lumber retaining wall is square by using the standard 3, 4, 5 measurement method. Begin by laying out the dimensions of the wall using the rebar stakes and string to form the layout of the wall. Then measure 3 feet from one corner and 4 feet from another and mark the measurements on the string. Next, measure the distance between the two marks and if it equals 5 feet, you have a right angle corner. The last step in the layout is to set a level string line at grade to use a reference for the top of the first course.

Step 2 – Set the First Timber

Excavate a 12 inch deep trench around the perimeter of the wall with the string acting as your guide. Next, compact the soil with the hand tamper and add 6 inches of the gravel compacting this as well. Before setting the timber, pre-drill the piece with the 9/16 inch drill bit placing 4 equally spaced holes the length of the timber. Set the timber in place and level it using the string line and torpedo level then stake it in place. Simply drive the rebar stakes through the pre-drilled holes with a sledge hammer to secure the timber. After this step has been completed, you can remove the string and use the first timber as your level point for setting the rest of the first course. 

Step 3 – Finish the Wall

To complete the lumber retaining wall just continue installing the first course using the rebar to stake the timbers in place. After the first course is in place fasten the second course to the first course using the impact driver and 12 inch landscaping screws.  When making the cuts for the end peices, it's often a nice design feature to leave the timber with a 45 degree angle cut.  When making any cuts, it’s always important to remember to apply wood sealer to any exposed areas of the timbers after to ensure a long lasting installation. Another important technique that helps build a sturdy wall is to stagger the seams in the wall by at least four feet. By following these methods, your lumber retaining wall will last for decades to come.