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9.19.1.3.(2)
OH1OS2
ObjectiveOH1 Indoor Conditions
Attribution
Application
Application 1: 
Clear air space between insulation baffles and the underside of the roof sheathing at the junction with exterior walls, in attic and sloped roof assemblies, 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 as stated in:
  • Sentence 9.19.1.1.(1), where attic or roof space venting can be shown to be unnecessary, and
  • 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 airflow through the vented space, which could lead to:
  • condensation in the space, or
  • the formation of ice dams, which could lead to the ingress of water.
This is to limit the probability of:
  • compromised thermal performance of components intended to provide resistance to heat transfer, which could lead to an inadequate control of the temperature of interior spaces,
  • water accumulation in interior spaces or an inadequate control of relative humidity,
  • the generation of pollutants from biological growth or from materials that become unstable on wetting, or
  • deterioration, which could lead to compromised integrity of ceilings acting as environmental 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.
Intent 2: 
To exempt junctions of sloped roofs and exterior walls where preformed baffles are installed from the minimum clear air space dimensions specified in Sentence 9.19.1.3.(1), based on the demonstrated effectiveness of a reduced unobstructed space provided by insulation baffles.
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