The cricket behind the chimney
A chimney passing through a sloped roof creates a problem on its uphill side: everything running down the roof arrives at a flat masonry wall and stops. The solution is a cricket, a small ridged structure built behind the chimney that splits the flow and sends it around both sides. On a great many older houses here, nobody built one.
- 1 Ridge caps. Thin, exposed, and worked loose by a winter of freezing and thawing.
- 2 The field. One layer or two, and the answer changes what a tear-off costs.
- 3 Valleys. Leaves mat where two slopes drain as one, and snow sits on top of them.
- 4 Flashing. Old masonry chimneys, and the saddle behind them that should shed snow.
- 5 The vent boot. A collar that goes brittle in the cold and splits without warning.
- 6 Eaves and ice dams. Where escaping attic heat melts snow that refreezes at the edge.
What happens without one
Water pools against the uphill face and sits there. Debris collects in the same spot and holds moisture between rains. In winter, snow drifts against the masonry and stays long after the rest of the roof has cleared, which means that one square meter spends weeks wet while everything around it is dry. Whatever flashing is there is asked to hold back standing water rather than to shed running water: a completely different job, and not the one it was designed for.
The failure shows up inside as a stain on the ceiling near the chimney, and it is routinely misdiagnosed as a flashing problem. Replacing the flashing on a chimney that needed a cricket buys a few years and the stain comes back, because the water was never being shed in the first place.
When it is required, and what to ask
Building codes generally require a cricket once a chimney reaches a certain width across the slope: roughly thirty inches is the common threshold, though the requirement is worth confirming with your own building department, since Connecticut towns administer this individually. Older houses predate the requirement, and plenty of newer re-roofs simply skipped it.
On any quote for a house with a wide masonry chimney, ask two things directly: is there a cricket now, and if not, is one included. It is framing and metal work rather than shingle work, so it is a real line item, and it is the difference between a chimney that stops leaking and a chimney that gets re-flashed every eight years.