How to compute a tree's critical root area

Protect tree roots during construction

It's vital to avoid disturbing or compacting soil around a tree that you want to preserve on a building site. The best way to prevent damage to a tree's root system is simply to fence out the critical root area -- that is, the area that contains the bulk of the tree's roots.

How to determine the critical root area:
1. Measure the circumference of the tree's trunk at 4-1/2 feet above the ground.
2. Divide the circumference by π (3.14) to determine the diameter of the tree's trunk.
3. Multiply the inches of trunk diameter by 1.5. (This gives you the critical root radius -- 1.5 feet for each inch of trunk diameter.)
4. Measure the critical root radius in all directions from the tree's trunk and compare the resulting circle to the tree's dripline. The larger of the two is the critical root area that should be protected.

Walking, driving, or piling construction materials within the fence should be absolutely prohibited. In addition, do not spill or allow runoff or buildup of chemicals, fuel, "cement water", sheetrock dust, etc. in the protected area.

Several university extension services have published some excellent information online about protecting trees during construction. These include:

• Preserving Trees in Construction Sites (pdf, 801K, Mississippi State University )
• Protecting Trees from Construction Damage: A Homeowner's Guide (University of Minnesota)
• Construction and Tree Protection (pdf 1.7MB, North Carolina State University)