I had a new roof installed 15 months ago. Because I switched to a ridge vent, I blocked my 2 attic gable vents with plywood nailed up over the vents from the inside. The 2 pieces of plywood are now covered in spots of black/grey mold. Any ideas on what could be causing this?
At first I thought it was a general attic moisture/vent problem. But there are no other signs of mold or moisture on the roof sheathing or trusses, or any wood in the attic. Only the plywood blocking the vents. Both bathrooms and the kitchen fans are vented up through roof vents and were replaced when I replaced the roof. My roofer swears I have enough soffit vents for adequate ventilation. Should I drill out some more soffit vents, anyway?
Then I thought maybe the plywood was already contaminated somehow. When I replace the plywood, should I install insulation on the inside and housewrap on the outside? What about painting the plywood with a good outdoor primer and paint?