Cross-Connection Air Gap (IPC Table 608.16.1)

The minimum air gap for the most positive backflow protection there is.

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Checked against published worked examples from: International Code Council (Louisiana LDH amended copy).

Details, formula, and sources

ScopeThe physical gap between a supply outlet and the flood-level rim, which nothing mechanical can defeat. IPC 2027 Table 608.16.1 (identical in 2021): 1, 1-1/2 or 2 in for effective openings up to 1/2, 3/4 or 1 in (1-1/2, 2-1/2 or 3 in near a wall), then twice the opening (three times within three diameters of a wall). A 1 in opening needs a 2 in gap (3 in near a wall); a 3/4 in opening near a wall needs 2-1/2 in, not 3 x 0.75. Checks a measured installed gap against the requirement. For indirect-waste and tank-fill protection. A design aid, not a substitute for the plumbing code adopted by your AHJ.

Formula or tableTable 608.16.1: opening <= 1/2 in -> 1 in (1-1/2 in close to a wall); <= 3/4 -> 1-1/2 (2-1/2); <= 1 -> 2 (3); over 1 in -> 2x (3x) the opening; required = near_wall ? air_gap_wall : air_gap; passes = measured >= required.

Source and editionIPC 2027 §608.16.1 and Table 608.16.1 (identical in 2021) (air gaps; 608.15.1 in the 2018 numbering) and ASME A112.1.2 (Air Gaps in Plumbing Systems) by name.

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 namesopening_in, near_wall, measured_in, air_gap_in, air_gap_wall_in, required_in

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