Mold on new plywood - perplexed!


Hello! Thanking in advance for any opinions. Had a new roof installed 5 years ago, with almost all the plywood replaced (there was poor ventilation prior). SmartVent was installed, plus a ridge vent, shingles are Timberline HD.

I don’t go into the attic much but just discovered that on only 1 side of the roof a massive area of mold on the plywood. Zero on the other side. (Both sides get sun if you’re wondering).

No bathroom exhaust fans vent into the roof. There is 16 inches of fiberglass bat insulation (I live in PA) 6" one direction 10" on top in other direction, none of it is blocking the Smartvents. Can’t imagine there is much heat loss.

I think my roofers are a decent company. We’ve been discussing but they say they’ve never had an issue with Smartvent and they do about 100 per year. They’re not dodging me but seem as perplexed as I am as to the cause.

Have any of you pros experienced something similar?


Need to post some Pics. Outside pics of roof and attic space both.