Water Enters Rooftop Duct or a Louver Plenum

Fast answer

Find the entry path and protect the system before sealing the first visible wet joint. Check temporary openings, louver and hood orientation, flashing interfaces, curb or plenum details, sealant condition, drain paths, and water carried from another trade or higher roof area.

What to check

1. Document where water is first visible and where it may be entering upstream.
2. Check caps, access doors, seams, penetrations, louvers, hoods, curbs, and roof interfaces.
3. Inspect insulation and liner for wet material that may require replacement.
4. Verify the approved weatherproofing responsibility and repair detail.

Do not

Do not trap water inside the assembly by sealing over wet insulation or blocking a designed drain path.

Ask the foreman

“Water is entering this rooftop duct/plenum. I traced the wet area past the nearest joint and checked the temporary cap, louver, curb, and roof interface. Do you want the system opened for a full water-path inspection before the exterior repair is made?”

Why it matters

Water can travel far from its entry point, damage insulation and finishes, contaminate the system, and reappear after the roof is closed.