Trees add beauty, shade, and value to a property, but planting them too close to a house can sometimes lead to foundation problems. While tree roots do not usually break through solid concrete, they may take advantage of existing cracks, dislodge the soil under a structure, and cause movement of the foundation. Certain tree species are more dangerous than others due to their size, root development, and water needs.
Understanding which tree roots affect foundations can allow home owners to make wise landscaping choices, avoid expensive repairs and safeguard their properties. This guide describes the most probable trees that may damage the foundation, how their roots impact the building, and what you can do to minimize the risk.
Willow Trees
Willow trees are among the trees most commonly associated with foundation and underground plumbing problems. They multiply rapidly and their root systems are widespread in search of water. Since willows need a lot of moisture, their roots tend to be drawn to water sources such as leaking pipes, drainage systems and moist soil around foundations.
Prevention tip: Avoid planting willow trees around your house, underground utilities, or drainage systems. Provide ample space to these trees.
Oak Trees
Oak trees are popular for their strength, shade, and long lifespan. However, mature oak trees can develop large, far-reaching root systems that extend well beyond their canopies.
Oak roots can also take advantage of existing weaknesses in older foundations, although they rarely penetrate sound concrete directly.
Prevention Tip: Plant large oak varieties a safe distance from your house, considering their mature size and the local soil conditions.
Maple Trees
Residential landscapes usually have maple trees due to their appealing foliage and shade. But some varieties have extensive, shallow root systems that may interfere with surrounding structures and hard surfaces.
Silver maples are especially worth consideration as they grow fast and can have extensive surface roots. These roots can raise sidewalks, driveways and patios. Roots can aggravate the damage in case they grow close to a foundation with pre-existing cracks or weak points.
The movement of the foundation may also be caused by the change in moisture content of shrink-swell clay soil by the uptake of water by the maple trees.
Prevention tip: When space is limited, select smaller varieties of maple, and do not plant large-growing varieties of maple near foundations and paved surfaces.
Poplar and Cottonwood Trees
Poplar and cottonwood trees are fast growing and have strong root systems that extend all over the soil. Their roots are also in search of moisture and thus they are particularly problematic around leaking water lines, sewer pipes and drainage systems.
Though these trees do not normally penetrate solid foundations, their roots can penetrate the existing cracks or joints in underground pipes. These weaknesses may be aggravated by root growth which causes leaks and other moisture variations around the foundation.
Prevention Tip: Poplars and cottonwoods should be kept at a distance of buildings and underground utility lines. Take into account the mature tree height and root spread.
Elm and Ash Trees
Elm and ash trees may have large root systems that compete with other buildings in the vicinity in terms of space and water. When trees grow in good soil, their roots can extend way beyond the trunks especially when the trees are mature.
Elms often develop extensive root systems and other forms of ash have powerful roots that may disrupt the sidewalks, driveways and other hard surfaces around them. Their roots can also take advantage of the existing holes around foundations and underground pipes.
Prevention tip: Before planting elm and ash trees around your residence, examine their size at maturity, and watch the trees that are already there, to see if they are moving the soil or damaging their structure.
How Tree Roots Damage Foundations
Tree roots can affect foundations in several ways. Understanding these causes helps homeowners identify potential problems before they become expensive repairs.
Soil moisture loss: Trees absorb water from the surrounding soil. In shrink-swell clay, this can cause the soil to contract and the foundation to settle unevenly.
Existing cracks: The roots can penetrate small cracks or weak joints and slowly increase the existing damages as they develop.
Underground pipe damage: Roots can enter leaking or damaged sewer and water lines, causing blockages and leaks that affect nearby soil.
Surface pressure: Large roots may cause nearby sidewalks, patios, and driveways to lift, but are less likely to cause direct harm to a well-built foundation.
Uneven soil movement: Different moisture levels around a building can cause parts of its foundation to move at different rates, potentially resulting in cracks and sticking doors or windows.
Common warning signs include widening wall cracks, uneven floors, gaps around doors and windows, and unexplained foundation movement. These symptoms may be caused by a number of factors, and serious or aggravating issues should be evaluated by a competent professional in the foundation.
How to Protect Your Foundation From Tree Root Damage
Preventing tree root damage starts with choosing the right trees and planting them in suitable locations. Before planting, research the tree’s mature height, root characteristics, and water requirements. Large trees generally need more space than smaller ornamental varieties.
In general, plant small trees at a distance of at least 10 feet, medium-sized trees at a distance of 15 to 20 feet. Depending on the type of soil and foundation, as well as the species, large trees can need 20 to 30 feet or more. These are approximated distances, not general safety regulations.
Other preventive measures are:
- Checking foundations, drainage systems and underground pipes on a regular basis.
- Fixing leaking pipes as soon as possible to prevent the roots in search of moisture.
- An arborist should be consulted before cutting or drastically pruning mature trees.
- Placing professionally installed root barriers where necessary.
- Checking the soil moisture in the area surrounding foundations, especially in long dry seasons.
Avoid cutting major roots or removing mature trees without professional advice. Sudden changes in soil moisture after tree removal can sometimes cause additional foundation movement.
