Maximum deflection of roof rafters, roof joists, roof beams and roof decking of plank and beam construction, ceiling joists, floor joists, floor beams, and floor decking, beams, joists and decking for balconies, decks and other accessible exterior platforms, in buildings to which Part 9 applies [see Sentence 1.3.3.3.(1) of Division A for application of Part 9].

To limit the probability of the excessive deflection of structural members.

Where framing supports or is part of an environmental separator, this is to limit the probability of the excessive deflection, deformation, displacement or failure of required environmental separation elements, which could lead to:

• precipitation ingress,
• air leakage, or
• 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.