Protecting a Large Douglas Fir During Construction

A homeowner plans an addition near a 100-foot, 2-foot-diameter Douglas fir, 10 feet from the new foundation. They intend to cover exposed roots with wet material and plastic, and use plywood to prevent compaction. They ask if this is sufficient.

Root Loss Threshold

A tree can tolerate loss of 25–30% of its root system before showing foliage dieback. The root zone extends roughly 1.5 times the branch spread. Overlap the construction footprint with the root zone; if more than 30% is severed, expect canopy decline.

Best Practices

• Cut roots cleanly with a sharp saw or loppers; do not tear.
• No need to keep cut ends wet – they will callus naturally.
• Protect the remaining root zone from all machinery. Erect a sturdy fence (not just plywood) at the drip line to prevent soil compaction.
• Do not add soil over roots – this suffocates them.

Consult an arborist on-site before construction begins.