How roots really grow
Most tree roots live in the top 18 inches of soil and spread well past the edge of the canopy. They follow water and air. They do not usually crack a solid foundation on their own, but they can take advantage of existing cracks and leaky sewer joints.
Clay soil and drought
Much of the area has clay soils that shrink as they dry. A large, thirsty tree close to a house can pull moisture from under the foundation during droughts, which adds to settling. Watering near the foundation in dry summers helps.
Planting distance
As a rule of thumb, plant large shade trees at least 20 feet from the house and small ornamentals at least 10 feet away. Keep willows and silver maples well away from sewer lines.
Should the tree come out?
If a tree is clearly damaging a sewer line or foundation, removal or root pruning may be needed. Root pruning a large tree can make it unstable, so it should be done carefully and only on one side.