Trap Arm Length

Maximum trap arm length by pipe diameter and slope.

Example

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Checked against published worked examples from: IPC.

Details, formula, and sources

Formula or tableTrap-arm horizontal length capped per IPC 2027 Section 909.1, Table 909.1 keyed to trap-arm size.

Source and editionIPC 2027 (International Plumbing Code). Section 909, Table 909.1.

Free accessFree read-only access at codes.iccsafe.org.

What governsEstimate. AHJ and licensed plumber / gas fitter govern. Verify against the IPC / IFGC edition adopted in your jurisdiction.

API field namespipe_diameter_in, slope_in_per_ft, max_length_ft, table_max_ft

Trap-arm slope and fall 1/4 in per ft for 2 in and smaller, 1/8 in per ft for 3 and 4 in (Table 909.1); total fall not more than 1 pipe diameter (909.2)IPC 2027 Table 909.1 / 909.2 (identical in 2021)

Details, formula, and sources

Formula or tableTrap-arm horizontal length capped per IPC 2027 Section 909.1, Table 909.1 keyed to trap-arm size.

Source and editionIPC 2027 (International Plumbing Code). Section 909, Table 909.1.

Free accessFree read-only access at codes.iccsafe.org.

What governsEstimate. AHJ and licensed plumber / gas fitter govern. Verify against the IPC / IFGC edition adopted in your jurisdiction.

Trap-arm slope and fall 1/4 in per ft for 2 in and smaller, 1/8 in per ft for 3 and 4 in (Table 909.1); total fall not more than 1 pipe diameter (909.2)IPC 2027 Table 909.1 / 909.2 (identical in 2021)