Chimney Cricket Calculator

Ridge Height, Run, Valleys and Flashing for a Chimney Saddle

The upslope face of a chimney is a dam: rain, meltwater, pine needles and shingle grit all arrive at that wall and stop, which is why wide chimneys without a cricket are one of the most reliable leak sources on any roof. A cricket, also called a chimney saddle, is a small two-plane structure whose ridge runs straight up the roof from the centre of the chimney and splits water around it. This calculator sizes that structure from three inputs: the chimney width measured across the slope, your main roof pitch, and the pitch you want for the cricket. It returns the ridge height at the chimney face, the run up the roof, the sloped ridge board length, both valley lengths, the valley metal to order with waste, the cricket sheathing area and an approximate step flashing count. It also tells you whether the chimney exceeds the 30 inch width at which codes normally require a cricket rather than flashing alone.