How flashing is supposed to shed water
Step flashing is woven into the roof courses along the sides of the chimney. Counterflashing covers the upper edge of those pieces on the chimney face. Water should step down the laps, not rely on a surface bead of sealant. Behind a wide chimney, a cricket or saddle turns roof runoff around the stack instead of letting it pond.
Why storm rain finds this joint
Wind-driven rain hits the uphill side and the vertical face, not just the shingles. Salt air thins exposed metal. Old tar patches shrink and split. A reroof that reused bent flashing or left counterflashing uncut can leak on the first hard storm. The stain indoors may appear hours later and several feet from the entry point.
If the mark only appears with a particular wind direction, write that down before the visit. That timing is more useful than a photo of the stain alone.
Flashing, crown, cap, and masonry
A flashing repair does not close a cracked crown, replace a missing cap, or fill open mortar. Those are separate scopes. Start from chimney leak repair if you only know that water appears after rain. Waterproofing does not reconnect lifted metal.
What the estimate visit sorts out
- Which layer failed: step flashing, counterflashing, cricket, or sealant-only patches
- Whether roof-field work belongs with a roofer
- Corrosion, mixed metals, and the condition of the masonry the counterflashing cuts into
- Whether a framed chase uses a different roof-to-siding detail than masonry