Excavation Near an Old Cypress: Protected Root Zone Calculation

How Close Can a Concrete Wall Be Built to an Old Cypress?

Planning a 10-foot-deep excavation and concrete wall tangent to the root zone of a mature cypress. Need to know safe distance.

Root Zone Facts

• 90–95% of roots in top 3 ft of soil; >50% in top 1 ft.
• Roots often extend 2× tree height beyond the dripline.
• Dripline (branch spread) is a minimum protection zone.

Protected Root Zone (PRZ) Methods

1. Dripline method: Protect area under canopy + as far beyond as possible.
2. Critical Root Radius (CRR): Measure DBH (diameter at 4.5 ft).
   Tolerant species (cypress): 1.0 ft radius per inch DBH.
   Example: 10″ DBH → 10 ft radius → 20 ft diameter PRZ.

Construction Guidelines

• Disturb ≤25% of roots within dripline for tolerant species.
• Avoid unnecessary damage; cypress tolerates root cutting better than many conifers.
• If space is limited, protect as much area beyond dripline as feasible.