To limit the probability that the flow of water down a roof's surface will be interrupted by a wide chimney, which could lead to a temporary increase in water depth beyond the depth protected by roofing or by the vertical leg of flashing at the chimney, which could lead to precipitation or meltwater ingress, which could lead to damage to masonry or to chimney liners from freeze-thaw stresses, which could lead to the escape of heat or flames, which could lead to the ignition of combustible building components, which could lead to damage to the building [see analysis for Sentence 9.21.4.6.(1)].