A friend asked me today about a house he was looking at. The drywall on the main level is stained black where the wall studs and ceiling joists are located and only on the exterior walls of the home. The home was built in the late 90’s and is a foreclosure…any ideas…thanks in advance…sorry for the poor pictures they were taken with his phone.
The wall studs are cooler and candle smoke and other pollutants condense more on them than the rest of the wall.
^^ what he said. Ghosting.
You can also call it “thermal bridging”.
As for the source, do not overlook the HVAC/furnace performance or other fuel fired appliances and fireplaces.
I agree Ghosting…I see it more often with homes heated with electric.