Evidence of a Roof Leak
What caused damage to the drywall on this ceiling (Figure 1)?
The damage is not due to a one time leakage. It is just too severe for a one time ice dam.
Climbing into the attic above the kitchen we found severe discoloration and delamination of the roof deck.
Note that the damage extends downward from the chimney. The lesser damage up slope is due to the protection afforded by the roofing paper. However, once the roof runoff infiltrated under the roofing paper it was able to infiltrate through the joint in the roof deck.
Roof leaks commonly evidence a path leading back to the source of the water entry.
Getting on the roof we found poor flashing where the roof meets the wall.
The cause is poor flashing.