Inspected a house today built in 1991. In addition to dark spots at the drywall nails and/or screws in the ceiling, there were also dark outlines of the ceiling joists in many areas of the house. In other words, you could easily see where most of the joists were located because those areas were darker than the rest of the white ceiling.
The roof had ridge vents as well as soffit vents and there were no indications in the attic, on the sheathing or rafters, of any excessive moisture.
Any ideas on what may have caused this?
I’ve attached pictures, but they don’t really show it well.