The Prescriptive Path method of tree protection establishes a root protection zone (see diagram at right) and blocks this zone from construction activities. The prescriptive path calls for the root protection zone to have a 1-foot radius from the center of the trunk per inch of tree diameter. For example, a 12-inch diameter tree would require a 12-foot radius root protection zone.
The root protection fencing must be a minimum of 6-foot high chain link fence secured with 8-foot metal posts, at the edge of the root protection zone. Existing structures and/or existing secured fencing at least 3.5 feet tall can serve as the required protective fencing. Place the yellow sign marked ‘Tree Root Protection Zone’ prominently on the fence designating the root protection zone and describing the penalties for violation. Install the fence before any ground-disturbing activities take place, including clearing, grading, or construction. Keep the fence in place until final inspection.
Encroachments in the root protection zone
Construction activities may encroach on no more than 25% of the root protection zone area. The encroachment may not be closer than one half of the root protection zone radius.
Installation of landscaping required by Title 33 is allowed within the root protection zone and is not an encroachment.
Prohibited activities in the root protection zone
Some construction activities are prohibited in any part of the root protection zone. These activities include:
- ground disturbance
- construction activity involving vehicle or equipment access (unless the access is on an existing street or driveway)
- storage of equipment or materials (including soil)
- temporary or permanent stockpiling
- proposed buildings
- impervious surfaces
- underground utilities
- excavation or fill
- in-ground irrigation systems
- other work activities
Cutting a large percentage of a tree’s roots can be dangerous. Most large tree roots, those over 4 inches in diameter, are structural roots that support the tree. If large roots are disturbed or removed, the tree may fall over and/or decline or die. Roots over 4 inches in diameter should not be cut. If cutting a tree’s roots is unavoidable, a certified arborist must approve and oversee the root cutting.