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9.20.6.4.(2)
ApplicationIntent
OS2OH1OP2OS1
ObjectiveOS1 Fire Safety
Attribution
[F61-OS1.2] Applies to assemblies required to provide fire resistance.
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 construction is required to provide fire resistance, this is to limit the probability of precipitation or meltwater ingress, which could lead to deterioration due to freeze-thaw stresses, which could lead to compromised fire resistance of the assembly, which could lead to harm to persons.
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