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.
Mold in roof attic.
Heating ventilation and air conditioning ducts may also.
This occurs when the temperature of the sheathing drops below the dew point creating a thin layer of moisture on the substrate.
Also notice the condensation stains at the shingle nail more evidence of a history of attic moisture which was a factor in this mold growth.
Insulation is often affected.
Mold growth on attic roof sheathing is a common issue in cool climates such as the pacific northwest.
The mold shown in the attic photographed above was identified as aspergillus sp.
Attic mold left unchecked can grow and lead to structural deterioration of attic sheathing and roof structural elements.
Particularly in cold climates when homeowners heat their homes in winter hot air tends to escape through the attic.
The chief cause of attic mold is poor ventilation.
Click photo for larger image.
There s an underlying moisture issue that needs to be resolved because mold requires moisture to grow and spread.
This occurs efficiently in attics with proper ventilation but attic mold can occur if the hot air meets the cold surface of the attic roof and creates condensation.
In the vast majority of cases the mold growth is caused by condensation.