If the sheathing either boards plywood or composite board along the lower edge of the roof is soaked and you can see a corresponding accumulation of ice on top of the roof ice damming is occurring.
Attic plywood wet.
Wet sheathing was found in attic area due to lack of venting.
Most attics are dry plywood is a smart vapor retarder with variable permeance.
2 layers of shingles.
Inner plywood of roof wet.
In this photo of very dark mold in an attic in a wet attic mold which we found to be brown in the microscope looked black on the plywood.
Attic insulation combination of fiberglass covered by cellulose.
The second variable is the species of wood used in the plywood.
It s not a vapor barrier.
Some woods are much more resistant to rot and fungal attacks.
Plywood is original 49 years old.
Not wet but some areas slightly damp.
Wanted to add more cellulose but installer said it would make wet roof worse.
Quite often the roof flashing is defective and needs replacement.
Attic venting attic moisture and ice dams.
What to do about a wet attic.
Even if conditions are conducive to mold growth elevated moisture plywood made from a fungal resistant wood will resist mold growth for quite a while.
Black mold in attics.
The attic vents provide a secondary method to help everything.