What Kind of Structural Damage Can Tree Roots Cause?

Subsidence

• Subsidence occurs with the decrease and then increase of moisture in soil underneath the ground surface. As the moisture level drops, soil compacts upon itself. As moisture is returned to the soil, it expands although not always to previous levels due to prior compaction.

  During dry periods, the roots draw upon more moisture than the soil may support. This problem causes the soil to dry out and then collapse. When the roots are underneath a structure, the soil underneath the structure moves downward away from the foundation. The weight of the foundation causes the structure to begin sinking. As moisture is returned to the soil, the soil expands, pushing upward against the foundation. As the contraction and expansion continue over time, sections of the foundation adjust to the movement differently. The material in the foundation weakens, causing fractures.

  As time continues, holes or pockets form within the soil as moisture evaporates and the soil fills with air. Under the weight of the structure above, the soil collapses into the pockets forming a subsidence underneath the building. Clay soils are most susceptible to this problem. Look around windows or doors for signs of subsidence as cracks form around them.

Drain Issues

• Tree roots seek out water to support the tree. Drains, underground water formations and seepage attract tree roots because they are a readily accessible source. As roots expand and extend to available resources, they can break through weakened pipes or drains. Water lines with cracks, poor seals, old rigid joints or any other cavities are prone to root invasion. Pipes or drains can burst as tree roots grow and expand within the drain field. Sewer lines and septic fields are commonly targeted by water-loving trees. Willows and maples are examples of trees that can break through pipes quickly.

Existing Damage

• Tree roots require an entrance into the structure to cause damage. Roots cannot break through solid brick, metal, plastic or other material unless the material is weakened to a point of fracturing under pressure. Foundations and pipes already damaged are most prone to root incursion. Roots can also move underneath structures with little or no foundation, such as sheds or garages. As tree roots expand, they lift these structures upward causing strain on the joints, seams and connecting hardware. The strain over time gives way, causing warping, fractures, cracks, broken seals and gaps in walls or roofing.

Prevention

• Most structural issues occur from the proximity of the tree to the structure. Roots can extend up to 150 percent farther than the overall height of the tree. If you have a 50-foot willow, the roots extend 150 feet underground from the tree. Plant trees far enough away from structures to avoid this problem. Avoid planting fast-growing trees such as willow, maple or poplar near water lines, septic fields or drains. Maintain adequate moisture levels in the soil to prevent it from drying out and compacting, thus avoiding the main cause of subsidence. Plant root barriers around older trees to keep roots from encroaching soil near structures. Determine pruning requirements of trees near structures by hiring a professional assessment to examine both the tree and the structure at regular intervals.