Example: a pop-top roof valley leaks into an old plaster ceiling

The situation

Illustrative example. Not a real job or customer.

A family owns a bungalow near the park that had a pop-top added years ago. The new second floor sits over the front of the house, and its roof meets the remaining original roof over the back rooms in a valley. Through a snowy winter, they notice a faint brown ring on the plaster ceiling of the dining room, which is toward the middle of the house. It grows slowly after each storm and melt.

1. The owners first suspect the upstairs bathroom, but the stain does not change after showers, and the water meter stays still with all fixtures off.
2. They notice icicles and a ridge of ice along the valley where the new roof meets the old, directly above a back bedroom, not the dining room.
3. A roofer inspects and finds that step flashing along the new wall was short in one area and that ice backing up in the valley pushed water under the shingles.
4. Water ran down the outside of the old wall framing inside the house, along a top plate, and pooled above the dining room ceiling before soaking through the plaster.
5. A restorer checks moisture in the ceiling, the wall cavity and the attic space, and finds wet insulation and damp framing along the path.
6. Wet insulation is removed and the framing is dried. The plaster ceiling, still firmly attached, is dried in place and later patched and painted.

The roof leak was fixed at the source, and only a small amount of plaster needed repair because the ceiling had not separated from its lath. The insulation removal and attic drying were the larger part of the job. The owners kept the roofer's photos and the moisture readings in case the claim needed them.