Where flashing is installed between a shingle roof and a chimney, to limit the probability of an inappropriate flashing configuration, which could lead to water spreading horizontally as it descends the roof slope and flowing beyond the area protected by the horizontal leg of flashing, which could lead to precipitation or meltwater ingress into chimneys, which could lead to damage to chimney liners from freeze-thaw stresses, which could lead to the premature failure of chimney liners, which could lead to carbon monoxide gas leaking into living space, which could lead to the acute poisoning or asphyxiation of persons.