Question
Jim. . .Similar problem as Laurie in Dallas: My Cypress is about 18-inches in diameter / 35-40 feet tall, and planted about 15 feet from the house. Surface roots and knees have been emerging for several years, but during the past 18-months large roots and knees have emerged right at the edge of the concrete slab, between the tree and the house. No roots or knees at all in open parts of the yard.
 Can root barriers be installed at the slab without causing terminal damage to my tree?

Answer
I do not think you will have any problem with the knees under the foundation. They need the oxygen to survive and moisture. The underside of foundations are dry soil and little oxygen. Cypress roots grow near the surface and if they find a wet spot they may start forming a knee. The knees are thought to be a means of supplying oxygen to the root system. Cypress tree knees are surface roots that swell in diameter, then grow upward. They do not grow downward so you can cut the root either side of a knee and it will easily pull out of the soil.

New Cypress knees may start to form in sidewalk cracks but not beneath a house foundation. Unless your foundation has major cracks and is sitting in the middle of a swamp, you probably don't have anything to worry about





The roots will spread about 1 1/2 times the width of the branches so you can gauge the closeness and if the roots will get to the foundation by measuring the width. You can install barriers along the foundation to stop the roots. Sounds like the tree is too close to the house. Bald cypress can grow large  50 to 70 feet in height with roughly 30 foot spread with the roots spreading to about 45-60 feet from the trunk. Here is a web link to root barriers. But i do not think that the knees will form below the foundation and cause any problems. IF the branches are reaching the house this will cause more problems than the roots by rubbing the house. http://www.4specs.com/s/32/32-9452.html

The root barriers will not cause damage to the tree--may get a very little foliage die back from the initial root cutting but after that the roots will grow along the barrier and cause not problems.