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9.19.1.2.(3)
OH1OS2
ObjectiveOH1 Indoor Conditions
Attribution
[F51-OH1.3] Applies to sloped roof assemblies that may be subject to ice damming.
Application
Application 1: 
Acceptable types and distribution of vents for attic or roof spaces, in buildings to which Part 9 applies [see Sentence 1.3.3.3.(1) of Division A for application of Part 9], where insulation is installed above the ceiling and below the roof sheathing.
Exceptions: 
except:
  • where attic or roof space venting can be shown to be unnecessary, and
  • as stated in Sentence 9.19.1.4.(1), which applies to the lower portions of mansard or gambrel roofs.
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Intent
Intent 1: 
To limit the probability of inadequate venting, which could lead to:
  • condensation,
  • the accumulation of moisture, or
  • the formation of ice dams.
This is to limit the probability of:
  • the ingress of water into attic or roof assemblies, or
  • compromised thermal performance of components intended to provide resistance to heat transfer.
This is to limit the probability of:
  • an inadequate control of the temperature of interior spaces or relative humidity,
  • the generation of pollutants from biological growth or from materials that become unstable on wetting,
  • deterioration, which could lead to compromised integrity of ceilings acting as environmental separators, or
  • water accumulation in interior spaces.
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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