This document describes measures to minimize construction impact. First, protect roots that lie in the path of construction. Approximately 90 to 95 percent of a tree's root system is in the top three feet of soil, and more than half is in the top one foot. Construction activity should be avoided in this area. Protect as much of the area beyond the tree's dripline as possible.
Some healthy trees survive after losing half of their roots.
However, other species are extremely sensitive to root damage even outside the dripline. It is more accurate than the dripline for determining the PRZ of trees growing in forests or that have narrow growth habits. Measure in inches. For each inch, allow for 1 to 1.5 feet of critical root radius. If a tree's dbh is ten inches, its critical root radius is 10 to 15 feet.