Intent 1:
To limit the probability of:
- water running down the face of masonry and entering
behind primary flashing, or
- the intersection being unable to accommodate differential
vertical movement of chimneys and roof surfaces, which could lead
to the displacement of or damage to flashing.
This is to limit the probability of:
- 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:
Where counter flashing is installed between a shingle
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)].