Poor Ventilation Termination
This harmless photo does not show the black mold/algae growth that was growing on the underside of this home’s roof sheathing. Older building code permitted the termination of mechanical fans from the bathrooms and kitchens at areas under the eaves as in this photo. Unfortunately under some circumstances this can cause moist air from the vent port to re-enter the attic space in through the soffits. The soffits on a home are designed to allow shaded cool air to enter the attic and replace the hot air that exits through the higher roof vents. Normally older systems are not overly problematic, but when the termination point of the fan is tucked up under in tight place like this one, it is tough for the moist air to go anywhere else than up into the attic. If you are in line for a new roofing project, it is a great time to relocate the termination points of the fan ducting if need be.