Question
Several years ago my neighbor planted Leyland Cypress trees on his side of our fence.  The tree trunks are 5 1/2 to 6 feet from my sidewalks and about 8 feet from my house.
I am noticing my sidewalks being raised and breaking apart, including the ones that are connected to my house.  Could the Cypress tree roots be the problem?

Answer
Yes it could be the roots. Leyland has the reputation of causing problems near walkways. Cypress trees have shallow root system and the roots will spread about 1 1/2 times the width of the branches. At maturity this may mean 20-feet. You can dig a trench along the walkway and install a root barrier that will cause the roots to grow deeper or turn from the walkway. This is too large a tree to be this close to the property line.

Here is a web link to root barriers. http://www.4specs.com/s/32/32-9452.html

You can ask your neighbor to move the trees and if he says no then I would treat my lawn along that fence line with a lawn fertilize called Weed and Feed. It contains a herbicide that will damage trees and kill the roots on your side. IF you have other trees nearby not wanting damaged do not use this.

Another way is install a root barrier along the property line and this will not let the roots grow your direction. IF I was going to dig a trench this is where I would think about digging. Without seeing the property this about about the best I can do.