All of our retaining walls are built using pressure treated lumber, unless you specify that you want redwood (if you plan to plant food products in the area). Posts are 4x4, 4x6 or 6x6. Many times a combination of 4x4 and 4x6 posts are used. We use 2x12 pressure treated boards to hold back the dirt.
We also offer a complete drain system for your retaining wall using three or four inch perforated schedule 40 pipe, or corrugated drain pipe. Both systems incorporate filter/weed fabric and 1 ½” drain rock.
