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.

This is to limit the probability of:

• compromised integrity of non-structural and structural components of the building, including ceiling membranes,
• for roof framing, rainwater ingress into or through assemblies, which could lead to deterioration, which could lead to compromised structural integrity of roofs or of building elements protected by roofs,
• for roof framing, ceiling joists or floor framing supporting air barrier materials, vapour barriers or insulation, condensation on interior surfaces or within assemblies or condensation of moisture from interior spaces, which could lead to deterioration, which could lead to compromised structural integrity of the roof, ceiling or floor or assemblies supported or protected by these assemblies, and
• excessive springiness or deflection of floor and roof systems,

This is to limit the probability of:

• the space being unsuitable for its intended use, or
• damage to the building.