Intent 1:
To limit the probability of:
- cracking, tearing or shrinking of built-up roof membranes
(when returned up walls at a sharp angle),
- interruption of roofing membranes at junctions with
walls or chimneys, or
- water temporarily ponding and eventually overtopping
cant strips.
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 the intersection is between a built-up 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 the premature failure of chimney liners,
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)].