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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.
A cricket, also called a saddle, is a small ridged structure built on the up-slope side of a chimney to split the water and send it around each side instead of letting it pond against the masonry. Code requires one on any chimney wider than 30 inches measured across the slope.
The cricket ridge normally runs from the centre of the chimney back up the slope, and the cricket sides pitch at least as steeply as the main roof so water sheds rather than sits. A common rule is that the cricket ridge height equals half the chimney width times the roof pitch ratio.
| Chimney width | 4/12 | 6/12 | 8/12 | 12/12 |
|---|---|---|---|---|
| 30 in | 5 in | 7.5 in | 10 in | 15 in |
| 36 in | 6 in | 9 in | 12 in | 18 in |
| 48 in | 8 in | 12 in | 16 in | 24 in |
| 60 in | 10 in | 15 in | 20 in | 30 in |
| 72 in | 12 in | 18 in | 24 in | 36 in |
These are the geometry figures. The cricket is framed, sheathed, then flashed and covered like any other small roof plane.
On any chimney more than 30 inches wide measured across the slope. That is a code requirement rather than a preference, and it applies to wide skylight kerbs and similar obstructions too.
It splits the water arriving from up-slope and sends it around each side of the chimney instead of letting it pond against the masonry, which is where the leak and the freeze damage otherwise start.
The ridge normally runs from the centre of the chimney back up the slope, with the cricket sides pitched at least as steeply as the main roof. A common rule sets the ridge height at half the chimney width times the roof pitch ratio.
No. Cement smeared against a chimney is a repair covering a missing detail, and it cracks within a few seasons. A cricket is framed, sheathed, flashed and covered like any other roof plane.
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