Trees will extract moisture from under a foundation by a process called evapotranspiration through their root system, which is especially problematic during times of drought since there is more moisture under a foundation than in the yard. When a foundation sitting on expansive clay is not constructed raid enough to resist differential movement and there is a decrease in moisture, the underlying clay soil will shrink, which results in consolidation and subsequent settlement. Studies completed in England show trees should be at least the mature height of the tree away from the building to prevent affecting the foundation. If, however, the tree in question is a willow or cottonwood tree, these studies show they should be at least twice the mature height away from the foundation.

Therefore it is important that trees not be allowed to grow close enough to adversely affect a foundation. To address this situation, the owner has two choices, remove the tree or install a root barrier between tree and house to lessen moisture fluctuation caused by the tree. If, however, the tree is so close to the foundation that cutting of roots will destabilize the trees support, the only option is removal of the tree.

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