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:

• compromised integrity of supporting soils,
• reaction with contaminants and chemicals in the soil,
• condensation, or
• moisture ingress from the ground.

This is to limit the probability of:

• deterioration, which could lead to compromised structural integrity of the separators or of elements supported or protected by the separators, and
• the freezing of soils on which foundations bear, which could lead to the displacement of structural elements.

This is to limit the probability of structural failure, which could lead to harm to persons.