Brand new home, never occupied, with a definite mold-like growth on the underside of all roof sheathing. Soffit vents w/baffles (none restricted) between all rafters, continuous ridge vent. No vents ducted into attic area whatsoever. I’ve run into this almost identical situation twice in as many weeks. Of course, I’ll report what I see and recommend further evaluation and treatment, BUT why do you think this is happening? The home is well built, has the required ventilation and insulation, but is still growing a “mold-like” substance in the attic; and, it’s never been occupied so will most likely get worse with time. Thanks in advance as I’m perplexed.
Could be the home is still drying out. Wet lumber, drywall mud joints, paint, concrete foundation all need time to dry. If home was closed up and not heated, it can have a lot of moisture inside working its way out through the roof.
What Linus said, especially with wet lumber (roof truss assembly) etc.