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9.20.6.4.(2)
ApplicationIntent
OS2OH1OP2OS1
ObjectiveOH1 Indoor Conditions
Attribution
[F61-OH1.1,OH1.2,OH1.3]
Application
Application 1: 
Minimum width of air space behind masonry veneer over wood-frame walls, in buildings to which Part 9 applies [see Sentence 1.3.3.3.(1) of Division A for application of Part 9], where:
  • the masonry veneer is not individually supported by the structural backing,
  • the masonry veneer is not in contact with the ground,
  • the wall height above the foundation wall does not exceed 11 m, and
  • the roof or floor assembly above the first storey is not of concrete construction.
Exceptions: 
except as stated in:
  • Sentence 9.20.1.1.(2), which applies to masonry walls other than those described above, or where the masonry is designed for specified loads on the basis of ultimate and serviceability limit states, and
  • Sentence 9.20.6.4.(4), which applies to masonry veneer required to be individually supported by the backing material.
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Intent
Intent 1: 
To limit the probability that extruded mortar will bridge the gap between the veneer and the sheathing membrane, which could lead to the accumulation of water on the sheathing membrane.
Where masonry units support or are part of an environmental separator, this is to limit the probability of excessive moisture transfer through masonry units, which could lead to:
  • precipitation ingress, or
  • compromised thermal performance of components intended to resist heat transfer.
This is to limit the probability of:
  • an inadequate control of temperatures of interior spaces, drafts, 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.
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