With its hidden, underground interaction, it is difficult to visualize what your tree roots are doing near your home's foundation. Although tree roots are inhibited by a common concrete foundation, they are typically forced downward as they strike the barrier. If you have a shallow foundation, coupled with unusual, moist soil under the house, it is possible for the roots to grow down and under your structure.
Root Growing Habits
Growing in the top 2 feet of soil, tree roots are not a mirror image of their canopies, but actually spread horizontally in search of nutrients, oxygen and moisture. When roots encounter a solid foundation, they simply turn downward. If your foundation has significant cracks, however, smaller feeder roots may enter the orifices. Although this may seem alarming, small roots cannot harm your foundation since they do not have the strength of a thick root structure to heave the concrete. In general, roots simply look for moist soil areas and prefer growing far from major ground barriers.
Tree roots do not need to interact with your foundation if you keep the surrounding soil around your structure dry. For example, flowerbeds located against your foundation encourages tree root growth toward the home, based on the available moisture. Maintaining dry soil around your home by moving the garden forces the roots to turn away from the foundation for sustenance. However, leaking pipes under a home easily entices tree roots to grow down and under the foundation for soil moisture. Well-maintained water pipes allow the ground under your house to remain dry and free from hungry roots.
Although foundations inhibit tree root growth, you can protect your structure's stability further with a root barrier. Typically, a plastic or metal sheet less than 1-inch thick inserted vertically into your soil; this barrier presses against your foundation's edge near the tree's location. Simulating the same inhibiting effect against the roots, the barrier forces roots downward, but they cannot continue under the foundation since the sheet is commonly much longer than the foundation is deep. As a result, your tree and foundation remain physically separated in the soil structure.
Foundation and Close Roots
It is possible to remove roots close to your foundation, as long as they are not large, anchoring growths that may harm the tree if removed. Using a shovel, simply remove some soil from the foundation's edge -- you may need to dig several feet to actually see the roots. Cut any smaller roots that are trying to grow into foundation cracks or seem to be growing down and under the concrete. If your tree is relatively large, you may need to excavate a large area to access all the offending roots.