Why is rooftop duct holding water on top?

Outdoor duct should not become a pond. If water is standing on top, check panel pitch/cross-break, insulation/weather wrap, support sag, and approved roof-duct detail before it rots or leaks.

['Flat rooftop duct can collect water if the top panel, supports, or weatherproofing do not shed properly. That water adds weight, bows metal, damages wrap, and eventually finds seams or screw holes.', 'Do not just patch the wet spot. Find why the water is staying there: flat top, sagging supports, missing pitched cap, damaged membrane, or bad slope. Likely recovery is a pitched cap/doghouse, cross-broken panel replacement, support correction, or weatherproofing repair per approved detail.']

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

• Ponding water can damage the duct, insulation, roof membrane details, and eventually leak into the building.

Steps

• Locate the ponding area and whether the duct top is sagging or oil-canning.
• Check support elevations, roof slope, top-panel shape, and insulation/weather membrane condition.
• Look for open seams, failed tape/mastic, fasteners, or water entry points.
• Check whether a pitched cap or shop-fabricated weather hood is required.
• Coordinate with roofer/foreman before cutting or rewrapping roof duct.

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