In the attic of this home that had recently been re-roofed, the roof sheathing and trusses were wet and near the eves they were ice-covered. This condition was more extreme toward one end of the attic. No damage to the ceiling was visible at the floor below. What is a likely source of this excessive moisture?
a. A water supply pipe burst in the unheated attic. The plastic vapor retarder installed above the ceiling drywall prevented water from saturating the drywall.
b. The furnace exhaust vent sections were not screwed together and separated when the roofers lifted the jack to remove the old shingles.
c. Improperly installed valley flashing allowed leakage that was spread through sheathing and framing by the concentration gradient force.
d. Improperly installed ridge vent allowed wind-driven rain from a storm approaching from the north to enter the attic.