How to Build a Strong Retaining Wall with 4x4 Treated Post

Three Parts:Laying the FoundationBuilding the First CourseConstructing the Wall

The instructions for building a retaining wall out of 4x4 treated post aim to help ambitious homeowners and do-it-yourselfers tackle this task. If you appreciate the satisfaction of creating visually appealing and utilitarian property features, start with step 1!

Part 1
Laying the Foundation

  1. 1
    Dig a level trench a foot deep into stable soil. Make the trench straight by staking out the location exactly and using a tight string to make a line between the stakes.
  2. 2
    Add 6” of sand or crushed limestone as a base leveling material. Compact the base material.
    • Check base material with a level or measure down from a leveled string line.
    • Add base material to low spots.
    • Repeat compacting.
  3. 3
    Level the trench from one end to the other.

Part 2
Building the First Course

  1. 1
    Begin 1st course with a full length 4x4 post. The word “course” means one row or one layer of the materials of which the wall is made.
  2. 2
    Drill two half inch holes through post centered 4ft apart.
  3. 3
    Hammer the post in place with rebar through the holes. Hammer rebar until flush with top of 4x4 post.
  4. 4
    Repeat for the entire length of the wall.
  5. 5
    Measure the last post needed. Transcribe measurement onto a post. Mark line around the post with speed square and pencil, and cut the lines with circular saw.
  6. 6
    Check each post level horizontally and plumb vertically as subsequent courses will be affected.
    • Add wooden shims if necessary.

Part 3
Constructing the Wall

  1. 1
    Begin the second course with a post cut to half-length to stagger the joints.
    • Check posts for level and plumb before nailing.
    • Use the 4 pound sledge to hammer 60d wall tie nails through the top of the post into the course below.
    • Install the wall tie nails every 16 inches.
    • Install full length posts to complete the course cutting only the end post.
  2. 2
    Begin third course/layer with ¼ length post to stagger seams. Keep going until the layer is complete.
  3. 3
    Begin fourth course with ¾ length post to stagger seams. Keep going until the layer is complete.
  4. 4
    Begin fifth course with full post again.
  5. 5
    Add T-braces to the wall while being constructed for support.
    T brace sketch
    • Dig a T shaped trench behind the wall.
    • Build the T-brace horizontally behind the wall with 4x4 posts.
    • Incorporate the base of the T-brace by nailing it flush in between two posts in a course of the wall.
    • Hammer rebar down through the T-brace into the ground.
    • Bury the T-braces.
    • Locate all T-braces below the top of the finished wall so as to not become disturbed or visible.
  6. 6
    Use the straightest and most visibly appealing 4x4 posts for the final top course the wall.
  7. 7
    Backfill the wall.


  • The foundation will determine how level and strait the wall will be and assist drainage and longevity.
  • Use straight posts only to build the wall.
  • Do not begin or end a course with short pieces as it may be unstable.
  • Factory cut ends of the posts should be placed at all visible locations such as the ends of the wall.
  • All cuts made on site will be placed at joints between posts.
  • Stagger the joints at corners on successive courses for strength and stability.
  • Bridge over the previous course’s seams to provide stability and aesthetics.
  • Use a long pry bar to separate post if nailed incorrectly.
  • Determine location for T-braces by the need for structural support.


  • Wear safety glasses always when working with tools.
  • Wear personal protective equipment such as leather gloves, safety-toe work boots with good traction, and a protective hard hat.
  • Wear ear and eye protection always when using a circular saw.
  • Work with an assistant as the materials and tools are large and heavy.

Things You'll Need


  • 4”x4”x8’ (or 12’ length) treated post
  • ½” x 24” rebar
  • 6” 60d galvanized timber ties (nails)
    6in galvanized timber ties
  • wooden shims


  • Spade shovel
  • metal rake
  • 4ft level
  • measuring tape
  • pencil
  • 2 wooden stakes
  • roll of string
  • string level
  • 4 pound sledgehammer
  • circular saw
  • speed square
  • cordless drill
  • ½” auger bit
  • large pry bar
  • tamper

Article Info

Categories: Walls Fences and Decks