While watching the carlise house, seg. 10 / 11 they were putting in a septic tank, and only spot was out back very close to a very large tree, they were concerned about root damange and killing the tree. They used a formula, as a rule of thumb, i would like to know that formula please.

Some thing like this: measure the trunk at chest high, 1/2 dia. eguals ???? and each inch equals a foot away from tree, is as close as you can come to be safe, from killing the tree. any help? mj