Where Chimney Leaks Really Start in Tinley Park: The Flashing

By Dan Joel, Elite Sweepers Inc.

A chimney passing through a roof creates a problem no other part of the house has: a rigid masonry structure penetrating a surface that expands, contracts and moves with every temperature swing. Something has to bridge that joint and keep it watertight through all of it. That something is the flashing, and when a homeowner reports a leak near the chimney, the flashing is where we look first.

What flashing is and how it works

The short answer: two overlapping layers of metal, one tied into the roof and one into the masonry, so water is always directed outward.

Step flashing consists of individual pieces woven in with the shingle courses as they run up alongside the chimney. Counter flashing is set into a groove cut in the mortar joints and folded down over the step flashing. The overlap is the whole design: water running down the masonry hits the counter flashing, is directed onto the step flashing, and from there onto the shingles and away. Neither layer works alone, and the joint is never sealed shut, because it has to accommodate movement.

Why it fails

The short answer: sealant was used instead of proper metalwork, or the metal has corroded, lifted or come out of its groove.

• Caulk as a substitute. The most common failure we see. A bead of sealant along the joint looks like a repair and lasts a season or two before it shrinks, cracks and lets water behind it, where it is now trapped.
• Corroded metal. Older galvanized flashing rusts through, often first at the low points where water lingers.
• Counter flashing pulling out. The mortar joint holding it deteriorates and the metal works loose, opening a direct path.
• Roof work done around it. Reroofing sometimes reuses old flashing or seals over it rather than properly reintegrating it with the new shingles.

How to tell flashing from a masonry leak

The short answer: where the water shows up, and when.

Flashing leaks typically appear at the ceiling right where the chimney passes through, and they follow rain closely: it rains, you get a stain. Masonry leaks, from a cracked crown or saturated brick, tend to show lower down, appear on the chimney breast itself, and often lag behind the weather because the water is working through absorbed moisture rather than running freely. A musty smell from the firebox with no obvious ceiling staining points more toward the crown or an uncapped flue.

None of that is conclusive from the ground, which is why the roof-to-chimney joint gets examined during a full chimney inspection.

Why catching it early matters more here than elsewhere

The short answer: water that gets behind flashing reaches wood.

Roof decking and framing sit directly at that joint. A flashing leak wets structural timber every time it rains, and because the water is behind the metal it dries slowly. By the time a ceiling stain is obvious, the decking has usually been getting wet for a while. This is the leak category where the delay between the problem starting and the homeowner noticing does the most damage.

Getting it repaired

Flashing work is covered on our chimney repair page along with the masonry side, since the two are frequently found together. If water has already been reaching the flue, our chimney relining page explains what that can involve. For local scheduling, see our chimney service in Tinley Park, with costs on our pricing page.

Elite Sweepers Inc is insured and bonded, works seven days a week from 7 AM to 7 PM, and gives you the price before starting. Call (708) 432-3977.

Published September 18, 2026