What are silt marks?
Silt marks occur when water rises and then slowly recedes leaving dirt and small debris that was mixed in or floating on the water clinging to the sides of vertical surfaces.
Silt marks observed along house foundations, support piers, drain pipes, and/or heating/cooling ducts is a result of rising water that has accumulated in residential crawl spaces and basements.
Wet basements and crawl spaces are sources of high humidity, which can produce surface condensation, mildew and fungi, musty odors, rust metal, and can become unhealthy.
Excessive moisture can cause deterioration of floor joists, beams, subflooring, insulation, electrical-mechanical systems and tilted piers. Moisture that seeps into heating and cooling ducts can lead to health issues... mainly spore growth inside the ducts and then carried throughout the house when the heat is turned on.
Prolonged water around support piers and house foundation walls can soften the soil and weaken their bearing capacity, increasing the possibility of foundation settlement, uneven floors, and cracking.
Home inspectors should be aware of silt marks as they investigate crawlspaces. They are typically an indicator of poor drainage control around the building or possibly a high water table during the rain season.
The inspection report should recommend further review by a licensed drainage contractor.