What is a Tree Protection Zone?

A Tree Protection Zone (TPZ) is the minimum area around a tree that must remain undisturbed during construction to protect critical roots, soil structure, and the trunk from damage.

How do I measure DBH (Diameter at Breast Height)?

DBH is measured at 4.5 feet (1.37 m) above ground level on the uphill side of the tree. Use a diameter tape or measure the circumference and divide by pi (3.14159).

What is the difference between TPZ and Critical Root Zone?

The TPZ is the entire protection area including the root system and growing space. The Critical Root Zone (CRZ) or Structural Root Zone (SRZ) is a smaller inner area where major structural roots anchor the tree.

When do I need a Tree Protection Zone?

Any construction, excavation, or land disturbance near existing trees typically requires a TPZ. Most councils and development codes mandate TPZ calculations when development is proposed within the drip line of protected trees.

Plant Reference

Tools & Calculators

Free Calculator

Tree Protection Zone Calculator

Calculate tree protection areas using US (ANSI A300) or UK (BS 5837) guidance. Australian calculations are paused while the current AS 4970 method receives qualified review.

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