Question
QUESTION: I have a ash tree in front of my yard, the roots are all protruding above the ground, they have damaged my driveway. The roots that are show 8 feet in diameter. My question is can I remove the roots above of the ground. will it be damage the tree.
How deep the roots of the ash tree toward to the ground ?

ANSWER: I am not sure what you mean by "8 feet in diameter" I am guessing you are talking about the width from the trunk and the spread of the roots not the diameter of the roots itself.
Cutting the above ground part of the roots will damage the root system. Up to about 25% of a root system can be removed without causing serious damage. I would cut the roots off along the driveway and install a root barrier . You will need to dig down about 12-18 inches deep along the drive to get all or most of the roots. The root system is mostly with in the first 2 feet of soil. The other exposed roots can be covered with sand if you do not cover more than 2 - 3 inches deep.  Here is a web link to the root barriers. http://www.4specs.com/s/32/32-9452.html



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QUESTION: Thank you for your immediately reply. I have one more question ,since the city already cut 1/3 of the roots, you mention that I can only up to 25% of a root system can be removed without causing serious damage, so I can not cut the roots off along the driveway. Can I remove the whole tree? but I really don't want do that for environmentally friendly reason.

Answer
The 25% is a guide. Additional root removal will depend on where the drive is in relation to the tree trunk. The roots will extend about 1 1/2 times the branch width so if you draw a circle around the tree where the branches extend to and you remove 1/3 of a slice though that pie shape the root can usually re grow and furnish enough food and water to the foliage if more than this is cut you will get some die back of the foliage and limbs but the tree will recover over time. Now if the drive is close to the trunk a cut will remove much more main roots than if the drive were near the edge of the branch width. Without seeing the tree and the drive it is difficult to tell for sure. I would try cutting along the drive and then fertilize the rest of the root system with 1 lb of 10-10-10 fertilizer per inch of trunk diameter scattered around the tree and watered in good--put the fertilize out just before a rain storm and you will not have to water it in. this will increase the growth of the remaining roots. IF the tree can not survive this cut you can always remove it later. But I think you will get some die back of the foliage but the tree will be ok with the fertilize treatment.