9.27.3.2.(1)

Intent 1:

To limit the probability that performance, with respect to strength, airtightness, resistance to liquid-water transfer and water-vapour permeance, will fall significantly below expectations.

This is to limit the probability of:

• excessive air transfer from the exterior through the assembly,
• precipitation or meltwater ingress through the second plane of protection, and
• the excessive accumulation of moisture transferred from the interior.

This is to limit the probability of the failure of required environmental separation elements, which could lead to deterioration, which could lead to compromised structural integrity of exterior walls, which could lead to harm to persons.