To resist the ingress of precipitation, water or moisture from the exterior or from the ground.

To limit moisture condensation.

To minimize the risk of generation of contaminants.

Ventilation of unconditioned and unoccupied crawl
spaces and *attic or roof spaces*, in *buildings* described in Sentence
1.3.3.2.(1) of Division A.

In attic or roof spaces, to limit the probability that inadequate
ventilation will lead to:

- the formation of ice dams, which could lead to the ingress into attic or roof assemblies of water backed up by ice dams, or
- the inadequate control of relative humidity, which could lead to condensation and moisture accumulation.

This is to limit the probability of harm to
persons.

In crawl spaces, to limit the probability that inadequate
ventilation will lead to condensation, moisture accumulation, or moisture
ingress from the ground.

This is to limit the probability
of the growth of mould and mildew, which could lead to:

- negative effects on the air quality of indoor spaces, and
- contact with moisture.

This is to limit the probability of harm to persons.