Do you have a water leak in your home? Is water dripping from your light fixtures or smoke detectors? If it is, one reason for this can be condensation.
As warm, moist air from inside the home rises up and comes in contact with a cold surface (like the underside of the roof deck), the air cools and moisture condenses out because cold air can’t hold as much moisture as warm air. That condensation forms a layer of frost on the cold surface.
When this frost builds up for weeks at a time and is followed by a warm day or two, it can melt all at once. Then, water will start running down the walls, out the bathroom and kitchen fans, through recessed light, out of door frames, etc.
People often jump to the conclusion that it’s a leak, even though it’s not raining and there isn’t too much snow to melt. But, what they are seeing is water that was already inside their home in the form of water vapor.
The best thing one can do to help this issue is control indoor winter humidity levels. If it’s 0°F outside, it’s best to maintain a humidity level of 20-25%.
WCCO recently released a story on this topic, too. Read more: http://cbsloc.al/2D6KxKi