Attic venting attic moisture and ice dams.
Attic plywood wet.
Wet sheathing was found in attic area due to lack of venting.
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.
The second variable is the species of wood used in the plywood.
Wanted to add more cellulose but installer said it would make wet roof worse.
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.
The attic vents provide a secondary method to help everything.
Plywood is original 49 years old.
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.
Some woods are much more resistant to rot and fungal attacks.
Quite often the roof flashing is defective and needs replacement.
The black attic mold shown here confirms that this attic had a serious venting and moisture problem including moisture from sources lower in the building.
Not wet but some areas slightly damp.
If any moisture makes its way to the plywood the damp plywood will dry out on hot sunny days.
2 layers of shingles.
As i m sure you know building codes require this type of attic to be vented.
Most attics are dry plywood is a smart vapor retarder with variable permeance.
What to do about a wet attic.
Black mold in attics.