I have a 2-1/2 story house. Kalcoated and painted since Aug 2002. In the 2nd floor exterior ceilings water spots (yellowing) is showing up at various spots around the house. The 2nd floor ceiling is fully boxed with the rafters sitting on top. Review in the attic area show no sign of water infiltration anywhere.
Poking a hole in the worst spot we found damp insulation near the exterior rim joist which is 14" away from the water mark. The 5/8 board was solid and show no signs of moisture except for the yellow mark.
These marks however seem to line up with the location of the ceiling joists - am I getting condensation through the joist - the joists are the newer t-joists