Trenching near a tree kills a large portion of the tree's roots. Tunneling under the tree does virtually no damage. Because most roots live in the top 18 inches of soil, a tunnel 2 feet underground often does little damage. However, placing the tunnel 3 to 4 feet deep is safer.
Tunneling under the roots is the best solution, but will add time and expense.
Tunneling under roots is only an option if there is enough slope remaing to the main sewer or test tee.
If, there is not enough slope, an ejector pump may be the solution. In this instance, an ejector pump may enable the sewage to be pumped to a higher evevation into a gravity pipe. In some cases the ejector pump may be used to connect to the mains test tee.
Russell v. Man
Facts: A contractor buys a vacant lot to build a residential improvement. A large pine tree straddles the common lot line with a neighboring property. A development code in the city forbids digging in a tree’s critical root zone. During construction, a trench is dug which cuts the roots of the tree owned by the neighboring property owner and kills it.
Claim: The neighbor seeks money losses from the contractor claiming the boundary tree died due to the contractor wrongfully and negligently cutting the roots creating a timber trespass onto the neighbor’s property which subjects the contractor to treble money liability.
Counterclaim: The contractor claims they injured the tree while on their own property, not while trespassing on the neighbor’s property and did not act maliciously and thus no treble damages can be awarded.
Holding: A California appeals court holds no trespass occurred on the neighbor’s property permitting treble damages but awards the neighbor the cost to replace the tree since the contractor’s negligence killed the tree by digging in a tree’s critical root zone, an unlawful act under city codes. [Russell v. Man (November 17, 2020) _CA6th_]
Trenching through roots will kill the tree!
Trees of course have roots to collect water and nutrients for the tree to grow. In the garden, tree roots can become a problem if proper consideration is not given to them when planting trees. Different problems can occur and these often depend on what type of tree you are growing. So when choosing trees and places to plant them, it pays to think about possible future effects of roots on your property, or that of your neighbors.
Most tree roots are in the top 12 to 24 inches of soil, with fine feeding-roots close to the surface. As roots grow they become thicker and close to the trunk they can be as thick as the branches on the upper part of the tree. Both the thick roots and the masses of smaller feeding roots can cause problems with pipes and pavements if trees are planted too close to them. How close that is will vary with different types and sizes of trees.
Although it is possible for some tree roots to break drainage pipes, the more usual problem is when pipes crack or joints fail with age or ground movement. Tiny roots then penetrate those cracks and joints, and multiply inside until the pipes are completely blocked. This will cause drainage water to back-up and it can lead to slow drainage, flooding and leaks. This is usually more of a problem with older pipes, as modern systems are much less likely to break.
The best long-term solution is to replace the pipes, but if this is not possible, mechanical routing is effective, but will need to be repeated regularly. Consider that the long-term costs of routing may be more than the cost of replacing pipes. Chemical products are also available that are put into the sewer, usually as foams. These are often effective, but follow the directions carefully or damage to your system or trees can occur.
Trees that grow best in damp conditions, like poplars, silver maple and willows, are the trees that most commonly block pipes.