If your Evanston home has a leak, the chimney is the first place to look.
The 1920s chimney problem
Most Evanston homes built between 1900 and 1940 have tall masonry chimneys with original lead step-flashing. Lead is a fantastic flashing material — soft, malleable, long-lasting — but it has a 70-to-90-year service life in our climate, and we are now at the back end of that for many homes.
What fails
The horizontal cap flashing (the top piece that lays against the chimney brick) corrodes through pinhole leaks. The vertical step flashings work loose from the mortar joints as the mortar weathers. Tar repairs (every homeowner has tried this at least once) seal the symptom for two seasons and then trap water behind them.
The correct repair
Two-stage flashing: new step-flashing woven into each shingle course in lead-coated copper, plus counter-flashing cut into the mortar joint and re-tucked with type-S mortar so the counter-flashing actually sheds water rather than caulks against it. Lifetime expectation when done correctly: 30–50 years.
What to avoid
Any contractor who proposes to "re-tar the chimney" — that is not a repair, that is a delay tactic. Any contractor who proposes face-mounted aluminum flashing with caulk — that is a five-year fix on a 50-year problem.
Cost of a proper chimney re-flashing on a typical Evanston chimney: $850–$1,650. Cost of not doing it: interior water damage, plaster repair, mold remediation, all the way up to ceiling collapse if it is ignored long enough.