A root barrier is an impermeable, strong structure installed underground for the purpose of preventing tree roots from damaging building foundations. Root barriers can be purchased from various manufacturers in materials ranging from plastic to steel, or can be made from scratch using concrete. In order to prevent most tree roots from jumping the barrier, it should be placed slightly above and slightly below the ground.
Measure a distance of at least 4 feet from the tree for placing the barrier. Dig a trench at least 18 inches deep and 12 inches wide. The length of the trench should expand 6 feet away from the tree in both directions.
Read the manufacturer's mixing instructions carefully and mix the concrete in a wheelbarrow.
Place the plywood boards on both sides of the trench and begin filling the trench with concrete. The concrete should come at least a quarter-inch above the surface to prevent the roots from jumping the top of the barrier.
Leave the concrete to dry for at least 72 hours before removing the wood boards. Once it is dry, carefully remove the wood boards and fill in the space with additional soil, pressing it down firmly with your feet.