Why Is My Chimney Leaking When It Rains?

1. Cracked chimney crown

The crown is the cement cap on top of the brick. Once it cracks, water goes straight into the chimney structure. It's the number-one source of chimney leaks in Massachusetts.

2. Failed flashing

Flashing is the metal seal where the chimney meets the roof. Old step flashing, dried-out caulk, or missing counter-flashing lets water run inside the roof deck.

3. Open mortar joints

Brick itself absorbs water, and eroded joints let wind-driven rain soak deep into the stack, eventually showing up in the attic.

4. Missing chimney cap

An uncapped flue is an open pipe. Rain falls directly into it, rusting the damper and staining the firebox.

5. Condensation

Sometimes it isn't rain at all — an unlined flue serving a modern high-efficiency furnace can create condensation that looks like a leak.

How to figure out which one it is

Note when the leak appears. Only during wind-driven rain points to brick and joints. Every rain points to crown, cap, or flashing. In dry weather, suspect condensation.

Frequently asked questions