9.26.4.8.(1)

Intent 1:

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, 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.

Intent 2:

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)], which could lead to harm to persons.