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9.4.2.4.(1)
ApplicationIntent
OS2OP2
ObjectiveOS2 Structural Safety
Attribution
[F20-OS2.1]
Application
Application 1: 
Minimum total specified load for ceiling joists or truss bottom chords in residential attics or roof spaces having limited accessibility that precludes the storage of equipment or material.
This applies to light-frame buildings to which Part 9 applies [see Sentence 1.3.3.3.(1) of Division A for application of Part 9], where wall, floor and roof planes are generally comprised of frames of small repetitive structural members, and where
  • roof and wall planes are clad, sheathed or braced on at least one side,
  • the small repetitive structural members are spaced not more than 600 mm o.c.,
  • the clear span of any structural member does not exceed 12.2 m,
  • the maximum deflection of the structural roof members conforms to Article 9.4.3.1.,
  • the maximum total roof area, notwithstanding any separation of adjoining buildings by firewalls, is 4 550 m2, and
  • for flat roofs, there are no significant obstructions on the roof, such as parapet walls, spaced closer than the distance calculated by:
    where
    Do
    = minimum distance between obstructions, m,
    Ho
    = height of the obstruction above the roof, m,
    Ss
    = ground snow load, kPa, and
    γ
    = unit weight of snow, kN/m3.
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Intent
Intent 1: 
To limit the probability of inadequate load-carrying capacity, where ceiling joists or truss bottom chords are not specifically designed to carry higher loads, which could lead to an inadequate resistance to gravity loads, which could lead to structural failure, which could lead to structural collapse, which could lead to harm to persons.
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