Heating ventilation and air conditioning ducts may also.
Mold in attic roof.
This occurs when the temperature of the sheathing drops below the dew point creating a thin layer of moisture on the substrate.
The most common cause of attic mold by far is blocked or insufficient ventilation.
What causes attic mold.
Improper exhausting of bathroom fans or dryer vents.
The photo at the left was identified as a toxic mold that probably should be removed although the ease of movement generally tearing off a roof and roof sheathing and perhaps roof framing to remove mold would not be sensible nor cost justified.
Dryer exhaust vents kitchen exhaust fans and bathroom exhaust fans.
Insulation is often affected.
If you have mold in the attic we recommend consulting with a mold removal specialist because.
Mold growth on attic roof sheathing is a common issue in cool climates such as the pacific northwest.