Most molds found in attics are commonly called mildew and are plant-like organisms that require food and moisture. Most attic mold grows in the cool seasons, because in the summer, it’s too hot in the attic, and the heat from the sun dries up any moisture on the sheathing or rafters. Paper, leather, cardboard, and even dust can support mold growth. It’s impossible to remove all foods for mold from an environment, but you can minimize moisture, which will prevent mold growth. 

Breathing in living or dead mold spores can cause health symptoms, so you don’t want mold to remain in spaces where you live or work. You don’t live or work in your unfinished attic, but if you enter or exit the space to access stored goods or check attic mechanical equipment, you can disturb mold growth, breathe in mold spores, and carry the spores back into the rooms below on your clothing, hair or shoes. 

With very few exceptions, mold does not degrade wood. Where wood has been dripping wet for weeks, however, due to roof or chimney-flashing leaks, wood-decaying fungi may be growing in the wood. If you see rotten or soft wood or even mushrooms in the attic, a contractor should evaluate the condition of the roof flashings and wood structure, and undertake repairs or replacement as needed. If the sheathing is seriously deteriorated due to leakage or condensation, some or all of it may have to be replaced.

Where Might The Mold Be Growing in an Unfinished Attic? 

Attic mold usually grows on the roof sheathing and gable-end wall sheathing or rafters, often worse on the north- or east-facing side, since these receive less sun and are therefore cooler. Mold spores may be trapped in exposed fiberglass insulation, if moldy sheathing has been disturbed by hammering done during roof-shingle replacement. Sometimes mold makes the attic smell musty, but often an attic can be full of visible mold growth that has little or no odor. 

Why Is the Mold Growing There? 

Attics are usually moldy because there’s too much moisture present and not because the ventilation is inadequate. Humid air can flow into the attic from the house through gaps around attic-access hatches or pull-down stairs, through openings in recessed fixtures located in ceilings below the attic, and through open or partially open louvers in a whole-house fan. Bathroom and kitchen exhaust fans that vent up into the attic or directly into the soffit space also introduce a lot of moisture. Mold can also grow in an attic because the roof is leaking.