Douglas Fir Roots Under House: Decay Takes Decades, Don't Accelerate

Roots of a 250-year-old Douglas fir cut 12 feet under your addition will decay in 10–20 years (dry, cool, low-oxygen under a house). Chemicals won't speed it meaningfully and risk indoor air quality.

Foundation Risk? Minimal

Decay is slow; footings won't drop suddenly. Cost of treatment outweighs theoretical long-term risk. Monitor for cracks, but don't excavate.

Natural Process

Fungi need moisture, warmth, air, wood. Under a dry house, moisture is limiting. Let nature take its course.