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9.23.4.5.(1)
ApplicationIntent
OS2OP2OH1OS1OS3
ObjectiveOS3 Safety in Use
Attribution
[F22-OS3.1] Applies to floors and elements that support floors.
[F22-OS3.7] Applies to walls, and elements that support walls, that contain doors or windows required for emergency egress.
Application
Application 1: 
Reduction in maximum spans for wood joists, rafters, lintels and ridge beams, in wood-frame constructions to which Section 9.23. applies [see Sentence 9.23.1.1.(1) for application of Section 9.23.], used to support roofs with roofing materials that are heavier than:
  • asphalt shingles,
  • wood shingles or shakes,
  • built-up roofing,
  • selvage asphalt roofing,
  • sheet metal,
  • glass-reinforced polyester,
  • hot-applied rubberized asphalt, or
  • polyvinyl chloride sheet.
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Intent
Intent 1: 
To limit the probability of excessively long spans, which could lead to roofs being unable to support additional loads imposed by heavier roofing materials, which could lead to excessive movement, deformation or damage to roofing.
This is to limit the probability of:
  • compromised structural integrity,
  • where elements support or are part of an environmental separator, the failure of required environmental separation elements, which could lead to deterioration, or
  • an inability to resist expected loads, which could lead to:
    • the excessive deflection or vibration of floors, or
    • the excessive movement or deformation of walls.
This is to limit the probability of:
  • compromised operation of doors or windows required for egress in an emergency, and
  • persons losing their balance, tripping or falling.
This is to limit the probability of harm to persons.
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