Step flashing for intersections of shingle roofs and masonry walls or chimneys, parallel to the roof slope, on buildings to which Part 9 applies [see Sentence 1.3.3.3.(1) of Division A for application of Part 9].

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, or
• compromised thermal performance of components intended to provide resistance to heat transfer.

This is to limit the probability of:

• an inadequate control of relative humidity, temperatures of interior spaces or water accumulation,
• the generation of pollutants from biological growth or from materials that become unstable on wetting, or
• deterioration, which could lead to compromised integrity of roofs or assemblies protected by roofs.

This is to limit the probability of:

• negative effects on the air quality of indoor spaces,
• the inadequate thermal comfort of persons, and
• contact with moisture.

This is to limit the probability of harm to persons.

Where flashing is installed between a roof and a chimney, to limit the probability of precipitation or meltwater ingress, which could lead to damage to chimney liners from freeze-thaw stresses, which could lead to flue gases leaking into living space, which could lead to negative effects on the air quality of indoor spaces [see analysis for Sentence 9.21.4.6.(1)].