What if heavy rectangular duct is sagging between hanger points?

Sagging heavy duct means the support layout is not controlling the load. Add or revise supports per the approved hanger schedule before joints deform or the run gets covered.

['Heavy gauge rectangular duct, smoke-control duct, lined duct, and large mains cannot be hung like light branch duct. If the joints dip between supports, the duct is telling you the spacing/support method is wrong.', 'The recovery is to verify the support schedule, add intermediate trapezes/rods, level the run, and recheck joints before sealing, insulation, inspection, or startup. Exact spacing and rod/strap size must follow the project/SMACNA/support detail, not a guess.']

Stop if

• Use this as training guidance. The foreman, approved drawings, project specs, manufacturer installation instructions, employer safety policy, and AHJ/code requirements always control the final answer.

Check

• Unsupported heavy duct can sag, leak, stress joints, fail inspection, or become unsafe overhead work.

Steps

• Identify duct type, size, gauge/weight, liner, fire/smoke rating, and pressure class if known.
• Measure support spacing and note where the joints or panels dip.
• Check whether added loads, insulation, or other trades are affecting the support system.
• Compare against the approved hanger/support detail.
• Add/adjust supports only under foreman-approved layout.

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