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IPC 308.6 Sway Bracing - Explained


Forum Coordinator
Oct 16, 2009
Somewhere Too Hot & Humid
Here’s an educational summary of IPC code section 308.6 on sway bracing:
  • Scope of the Code: Applies to horizontal drainage or waste pipes that are 4 inches (102 mm) or larger.
  • Conditions for Bracing:
    • Bracing is required where a pipe fitting changes the flow direction by more than 45 degrees.
    • This is to counteract the forces generated by the change in flow direction, which could otherwise move the pipe.
  • Nature of Flow and Forces:
    • Wastewater flow in large pipes (4 inches and larger) can surge significantly, especially when multiple smaller branches discharge into them.
    • These surges create waves of high flow, impacting fittings and potentially causing movement in the direction of flow.
  • Consequences of Unbraced Fittings:
    • Direction-changing fittings may move, pulling the upstream piping with them.
    • This lateral movement can lead to "swaying" of downstream piping, potentially causing failure in pipe couplings and connections.
  • Rationale for Bracing:
    • Rigid bracing or similar supports are mandated to prevent the upstream pipe and its fittings from moving in the direction of flow.
    • This ensures the downstream piping remains stable and does not sway sideways.
  • Exceptions to Bracing Requirements:
    • Upstream bracing is not required where the flow direction changes into a vertical pipe. Vertical pipes are supported differently and do not sway side to side.
    • The code does not apply to buried piping, as the backfill provides necessary support to prevent movement.