A chimney cricket, also called a saddle, is a small peaked structure built into the roof on the high, or uphill, side of a chimney to divert water around it instead of letting it pool against the back wall. It is often required by code on wider chimneys where a flat, wide swath of roof would otherwise dam water behind the chimney. A cricket is framed and flashed like a miniature roof valley on each side, feeding water around the chimney and back into the main roof slope.
A chimney sitting on a sloped roof blocks the natural downhill flow of water, and the wider the chimney, the more water backs up against its uphill side during a hard rain.
A chimney cricket solves that by building a small peaked ridge directly behind the chimney, splitting the water flow into two channels that route around each side of the chimney rather than pooling against it.
Each side of the cricket functions like a miniature roof valley, complete with its own flashing, feeding the diverted water back down into the main roof slope below the chimney. Debris that would otherwise collect against the chimney's back wall gets carried down the same channels instead of building up in place.
Most codes and manufacturer guidelines require a cricket once a chimney reaches a certain width, since a wide, flat chimney back without one creates a debris trap and standing-water risk almost by design, and that risk only grows as the chimney ages and its mortar joints weather.
Because a cricket combines flashing, framing, and shingle work in a small, tightly detailed area, it is one of the trickier parts of a roof to build or re-roof correctly, and it is easy for a rushed crew to skip or shortcut.
Leaks on the uphill side of a chimney are a common, often overlooked failure point, frequently blamed on the chimney itself when the cricket is the real culprit. A wide chimney with no visible cricket behind it, or a cricket with worn flashing, belongs on the inspection list.
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