What Are These Black Stains On The Walls? Understanding Ghosting On Walls vs. Mold

Oftentimes, inspectors and contractors will receive phone calls from homeowners who describe a mold problem that has recently developed on the walls and ceilings of their homes. Sometimes, they describe the mold patterns as black stains on the walls and ceilings that seem to be following the framing of the house. The good news for these homeowners is that the stains do not mold and they are unlikely to present a health hazard to the occupants or a structural hazard to the building. The problem they are describing is called “ghosting” or “thermal bridging,” and, though innocuous, it can be a nuisance.