Roots of trees often straddle legal boundaires. For the most part few people are aware of the roots on the basis of "out of sight; out of mind" and they cause few problems. However tree owners have no rights to use neighbouring land to support their trees, and once damage is done to the neighbouring property, whether it be drains, walls, driveways or even foundations to property, leading to cracks and worse the questions that arise are "What can I do and who is going to be pay for the repair?" by the damaged property owner, and "What should I do with the tree?" by the tree owner.
Keep talking and be reasonable are the first steps. How much repair work is necessary (and what proportion of the damage is due to tree activity, rather than due to wear and tear), and how much might tree removal cost? Using solicitors and threatening court action, coupled with the necessary expert's report(s) is never cheap so minor damage may be best repaired and the tree owner "put on notice". Claims for negligence and nuisance require the damage to be foreseeable (in the legal sense) so evidence that the tree owner has been made aware of the problem and has not "abated the nuisance" are highly desirable. Diaries and dated photos of events can be useful if the issue escalates.
If the trees remain will the damage reoccur and who then is responsible? With the reoccurrence of damage tree removal is likely to be necessary. If evidence of the first incident is available, the tree owner may be liable for the cost of repair, especially if little or no tree work has been undertaken.
As the owner of damaged property, getting your building insurer involved is probably necessary whether you like it or not. If you did not let them know and the problem gets worse your insurance contract may have a get out clause. Similarly the tree owner should let their liability insurer (possibly through their contents insurance) know if they receive documents describing a possible liability.
Duramen Consulting can advise on the various issues that arise when tree roots are thought to be causing problems.