While Icicles look somewhat magical and remind us that winter has arrived, they are in fact an indication that something is wrong in that home. Usually that something is the dreaded ice dam.
Let me give you a definition of an ice dam and why it occurs: An ice dam is a block of ice that forms at the edge of the roof preventing the melting snow from properly draining off the roof. The melted water backs up behind the ice dam and remains a liquid. Since roofing systems are designed for water to run downhill rather than up, the water will find a path of least resistance to escape, and it finds cracks and openings in the exterior roof into the attic through the walls and ceiling.
If you have an ice dam, there is very little you could have done to prevent its formation. Even though code requires that roofing underlayment be installed 24 inches from the eave, it is merely a preventive measure rather, than a guarantee, that water will not back up and find a way into the interior. As heat rises, the air in your attic is warmest at the top and coolest at the eaves – and that is why snow on the roof will begin to melt first at the top and refreezes when it reaches the cooler eaves.
Because damage from ice dams is not covered by either roofing contractors or manufacturers, if you have interior damage, please contact your insurance company immediately. Do not make arrangements for repair until the ceilings and walls are dry. Take pictures of the interior damage, but under no circumstances try to get on the roof.
To help avoid ice dams, make sure your attic is well insulated and properly ventilated.
Once an ice dam forms, there is nothing you can do – it will normally go away on its own. About all you can do is arm yourself with buckets, mops and tarps for the furniture.