5.1.1 Describe the function of each of the barrier systems in the building envelope
Air Barrier: Designed to reduce the outward migration of moisture laden air through the envelope structure and reduce the inward migration of cold air. Reduces heat loss, moisture movement and infiltration. Needs to be 100% continuous, with all gaps sealed and impermeable to airflow. Code requires air permeability of no greater than 0.02 L/s-m2@75 Pa
Vapour Barrier: Slows the diffusion of interior water vapour into insulated exterior assemblies and helps prevent condensation of water vapour on cold surfaces in these areas. Needs to be allowed to dry. Does not need to be continuous but must cover most of the area. Code requires no greater than 60 ng/(Pa.s.m2)
Moisture barrier: Used to deter moisture from traveling through the exterior assemblies by way of capillary break, often used on foundations and roofs.
Weather/wind barrier: Sheds moisture to restrict water entry from the exterior, allows moisture trapped in the assembly to escape to the exterior, acts as a wind barrier to restrict air movement in the wall assembly
Thermal Barrier: Prevents heat loss by way of conduction. Creates a thermal resistance layer. (R-value)
