PHANTOM ROOF LEAKS

As a roofing contractor for 35 years in the Denver area, I often got calls about leaky roofs after a big snowfall and low temperatures. In fact, all of those “leaks” were due to condensation. The problem starts with warm, moist air that migrates into a cold, poorly vented attic. As trapped water vapor condenses, it freezes, most visibly on metal surfaces. When this ice eventually melts, the water finds a way to “leak” into the house. The problem is more common in a low-humidity area like Denver, where whole-house humidifiers introduce large amounts of moisture into the home. Something similar happens around bath fans. Here the likely culprit is an uninsulated metal exhaust duct near a cold roof. As moist air passes through the duct, the moisture condenses and freezes. When warmer weather melts the ice, “leaks” appear, usually as a ceiling stain near the fan.