How to Build a Timber Retaining Wall

Gravity is the constant enemy of any sloped yard, pulling soil downward and turning tidy landscapes into muddy washouts. A timber retaining wall acts as a structural dam, holding the earth back while adding clean, architectural lines to your property. When built correctly, these walls redirect water and create usable, level space where there was once only an unusable incline. Success here relies entirely on your foundation and drainage. If you ignore the pressure of saturated soil, your wall will bow or collapse within a few seasons. Done well, this project is a lesson in patience and proper backfilling; a well-constructed wall should be level, perfectly anchored into the hill, and drained so efficiently that water never has a chance to push the timbers out of place.

  1. Dig Your Foundation Trench. Dig a trench along the base of your slope that is at least 12 inches wide and 8 inches deep. Ensure the bottom is level from side to side and follows the grade if necessary, compacting the soil firmly once the trench is clear.
  2. Lay the Drainage Foundation. Fill the bottom of your trench with 4 inches of crushed angular gravel and tamp it down until it is rock-hard. This provides a stable, free-draining foundation that prevents the wood from sitting in standing water.
  3. Anchor the First Course. Place your first row of 6x6 pressure-treated timbers into the trench, checking them for level both horizontally and front-to-back. If the wall is long, stagger the joints of each timber so they don't line up vertically, which adds structural integrity.
  4. Pin Courses with Rebar. Stack the subsequent courses of timber, offsetting the joints at least 2 feet from the course below. Secure every layer by drilling through the top timber into the one below and driving 18-inch lengths of #4 rebar through the holes.
  5. Install Drainage Behind Wall. Place a 4-inch perforated drainage pipe behind the first course of timbers, surrounding it with clean gravel. As you build each layer up, continue to fill the space between the wall and the hillside with gravel to allow water to move freely to the pipe.
  6. Cap with Clean Lines. Once the wall reaches your desired height, secure the final course with countersunk heavy-duty landscape screws rather than spikes for a cleaner, finished look. Ensure the final timber is flush and level to create a clean visual cap.