The roof was one layer standard 3 tab shingle about 10 years old. Gable/moderate slope.
House had soffit/gable/roof top venting. Insulation was loose fill about 6-9 inches. No moisture stains in attic, ventilation seemed to be adequate.
So what is causing the stains around the vents?
How would you report the scenario?
Would an active vent like a power vent be an solution? Or maybe adding more soffit vents. (There were no baffles installed but the insulation was not blocking the vents.
I don’t know. It looks like some kind of airborne particulates coming out of the attic plated out on the shingles. The source of the particulates?
What’s the fuel for the heating system?
Did any exhaust flues terminate in the attic, including bathroom vents?
Was there a whole-house fan?
Was there any discoloration of wall or ceiling surfaces in the living space or of framing or sheathing in the attic?
If moist air was evacuated through the roof vents, it could be algae, although if those roof vents were galvanized and that was algae, there would be clear streaks on the downhill side from runoff, since algae doesn’t like zinc.
Good question Kenton. Looks like an unexplained anomoly to me. If there was no dicernable damage I might not call it out, or you might recommend to monitor it.
Fireplace in the basement back-drafted and sent all the smoke up through the attic. Since it was cold the particulate settle out around the vents. Owner probably opened the basement windows to get the smoke out and up the smoke goes finding any exits into the attic. The reason may be that they did not get a hot enough fire to start heating up the chimney.
JMEG