Below-ground, exterior environmental loads presumed to bear on building materials, components, assemblies and their interfaces described in Sentence 5.1.2.1.(1) that are installed in buildings to which Part 5 applies [see Sentence 1.3.3.2.(1) of Division A for application of Part 5].

This also applies to the position of low air and vapour permeance materials within the building assembly relative to the position of materials providing thermal resistance in the assemblies of buildings to which Part 9 applies [see Sentence 1.3.3.3.(1) of Division A for application of Part 9], where the building assembly:

• incorporates low permeance materials that act as other than cladding or that are installed on the warm side of the assembly, and
• is more susceptible to condensation [see Sentences 9.25.1.2.(4) and (5) for combinations of interior and exterior environmental conditions that create a higher risk for condensation].

This also applies to the design of vapour barriers in buildings to which Part 9 applies [see Sentence 1.3.3.3.(1) of Division A for application of Part 9], where the building assembly is more susceptible to condensation [see Sentences 9.25.4.2.(2) and (3) for combinations of interior and exterior environmental conditions that create a higher risk for condensation].

To limit the probability of using incorrect assumptions regarding below-ground environmental loads, such as temperature, vapour pressure, hydrostatic pressure, and soil gas concentrations, in the design of environmental separators, which could lead to inadequate performance or premature failure under expected environmental or structural loads.

This is to limit the probability of:

• air transfer from the ground,
• condensation,
• precipitation ingress,
• moisture ingress from the ground, or
• pollutant ingress, including soil gas, combustion products from parking garages, or particulates.

This is to limit the probability of:

• the inadequate control of temperatures of interior spaces, relative humidity or water accumulation,
• the generation of pollutants from biological growth or from materials that become unstable on wetting, or
• deterioration, which could lead to further compromised integrity of environmental separators.

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.