Where the intersection is between a shingle roof and a chimney, to limit the probability of precipitation or meltwater ingress into chimneys, 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 harm to persons [see analysis for Sentence 9.21.4.6.(1)].