This ceiling stain is not an uncommon problem in many homes that have uninsulated metal ducts or flexible foil or plastic exhaust ducts that have an exterior exhaust vent cover without the webbed pest guard. In this case, small birds were able to enter and found the exhaust vent duct a safe place to nest. The birds broke through the flexible foil vent duct and made a cozy nest in the insulation.Unknowing to the home owner the damaged duct no longer exhausts the the moist air to the exterior but now into the attic. The moist air condenses when in contact with the cooler attic air and uninsulated metal duct section to form water droplets in the local area of the exhaust discharge and drips from the vent duct onto the attic side of the drywall. Over time, the condensation soaks through the drywall forming a visible stain on the bathroom ceiling. Apart from the visible ceiling stain this condition can also cause attic mold to form on the roofs under sheathing in this area. To prevent this situation from happening in your home it is recommended replacing the temporary flexible foil or plastic type duct with a permanent installed metal duct that is properly secured with a protective exterior webbed vent cover to prevents access by birds or rodents.The cost difference between metal and flexible ducts is only a few dollars and much cheaper and less frustrating than the repair the home will be face with in this situation.

 

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