Question
Can Cypress knees and there root system break concrete and get under a foundation as the root system of a Oak tree does?

Answer
Yes. This is a tree that will have root problems in a yard situation. In fact you may in the future experience cypress knees growing form the roots. Two major type problems--roots on the top of the ground making unlevel ground for mowing and roots that may cause "foundation cracks." The first area can be leveled by adding a soil layer over the roots (do not add more than 2 inches. The other "cracking" issue can be handle by root pruning the roots on the foundation side by trenching near the foundation (between the tree and the foundation maybe in this case about 4 or so feet from the foundation say about a foot deep) and this will cut the roots and keep them from getting under the foundation. The trench does not have to be kept open but fill it with soil and every 3-4 year retrench to cut the roots that may have grown across the original tench. Or install a root barrier along the foundation.