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5.5.1.1.(1)
ApplicationIntent
OH1OS2
ObjectiveOH1 Indoor Conditions
Attribution
[F63-OH1.1,OH1.2]
Application
Application 1: 
Properties and position of materials and components subject to differentials in temperature and water vapour pressure that are installed to:
  • provide resistance to vapour diffusion through building assemblies, and through interfaces between assemblies, or
  • permit the venting of vapour to the exterior.
This applies to 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].
Application 2: 
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].
Application 3: 
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].
Exceptions: 
except as stated in Sentence 5.5.1.1.(3), which applies where a lack of resistance to vapour diffusion or the inadequate venting of vapour will not adversely affect health, safety, the intended use of the building or the operation of building services.
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Intent
Intent 1: 
To limit the probability of
  • the inadequate control of vapour diffusion (except the diffusion of moisture from the ground) through environmental separators under expected environmental loads, or
  • the inadequate venting of vapour to the exterior.
This is to limit the probability of the accumulation of condensation, which could lead to:
  • the generation of pollutants from biological growth or from materials that become unstable on wetting, or
  • deterioration, which could lead to compromised integrity of environmental separators.
This is to limit the probability of:
  • negative effects on the air quality of indoor spaces, and
  • the inadequate thermal comfort of persons.
This is to limit the probability of harm to persons.
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