Where the shingle roof slopes upwards from a masonry chimney, to limit the probability of an insufficient upwards extension of flashing, 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)].