Why this junction fails
A chimney passing through a roof creates a joint that has to flex slightly with the building while staying watertight, and lead flashing here can crack, lift or corrode over time.
Common flashing problems
Lifted step flashing, a cracked lead apron, or flashing that's simply come away from the brickwork are the most frequent causes of leaks we trace back to the chimney.
Repair vs full replacement
Minor lifting can sometimes be re-dressed and re-secured, but flashing that's cracked, split or badly corroded is more reliably fixed with a full replacement in fresh lead.