‘Moisture is a roof’s biggest enemy.’ -- “Eventually, no matter what type of roof, the ravages of freeze-thaw cycles, rain, summer sun, blustery winds and all the rest of Nature’s arsenal take their toll. Leaks develop in the best of roofs over time, causing U.S. building owners to spend more than $12 billion annually on repairing, recovering or reroofing...[M]oisture is a roof’s biggest enemy. Moisture degrades the mechanical integrity of the insulation system, corrodes metal components such as fasteners and metal decks and adds excessive weight to the roofing system. And wet roofing also increases energy losses up to 70 percent because wet insulation loses its thermal resistance. An assessment performed by the Oak Ridge Lab shows that if low-slope roofing systems could be kept dry, more than three-fourths of a quadrillion BTUs of energy [equal to approximately 120 million barrels of oil] could be saved annually in the United States.”

Reroofing: How Wet Is Too Wet?, Rita Tatum, Building Operating Management, February 2001