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9.4.2.2.(1)
ApplicationIntent
OS2OP2OH1
ObjectiveOH1 Indoor Conditions
Attribution
[F22-OH1.1,OH1.2,OH1.3]
Application
Application 1: 
Specified snow loads on roofs of light-frame constructions 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, regardless of 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.
This applies to buildings to which Part 9 applies [see Sentence 1.3.3.3.(1) of Division A for application of Part 9].
Exceptions: 
except:
  • as stated in Sentence 9.4.2.2.(2), which applies to the minimum specified snow load, and
  • as exempted in Sentence 9.4.2.2.(3), which applies to bow string, arch and semi-circular roof trusses having an unsupported span greater than 6 m.
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Intent
Intent 1: 
To limit the probability that inaccurate snow load assumptions will lead to assemblies being unable to resist gravity, snow and rain loads.
This is to limit the probability of excessive movement, deformation or damage to roofing, which could lead to:
  • precipitation ingress, or
  • air leakage, which could lead to compromised thermal performance of components intended to provide resistance to 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 compromised integrity of environmental separators or of elements protected by such 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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