A cricket or saddle is typical on a chimney and is required by many authorities when the chimney width is more than 30 inches. The cricket or saddle is a peak that deflects water and snow around the chimney, preventing it from accumulating against the top side of the chimney. The cricket usually is made of the same material as the roof sheathing (plywood or waferboard in modern construction). Where no cricket is used, the top flashing should extend at least one-sixth of the chimney’s width up the chimney (6 inches minimum) and should extend up the roof under the shingles to a height that is equal to the distance the other end of the flashing extends up the chimney (some say 18 inches).
All of the base flashings are fitted against, but not attached to the masonry.