Attics are prone to moisture intrusion from a number of sources. These include leaks in the roof, leaks around plumbing vent lines, water from clogged gutters, improper or insufficient ventilation. Moisture buildup in a attic can result in mold or the rotting of the roof sheathing. It can also be detrimental to anything organic stored in the space. If you have a moisture issue in an attic and attic air is allowed to enter the structure below it either through the attic access point or the HVAC duct work or other penetrations, it can affect the indoor air quality in the building.