Ice Dam Removal & Prevention

It starts inside the house. Warm air leaks up into the attic and heats the upper part of the roof just enough to melt the snow sitting on it. The meltwater runs downhill until it reaches the eaves, the overhang past the outside wall, where there is no warm attic underneath. There it freezes. Night after night the ice builds into a ridge. That ridge is the dam.

Now the next round of meltwater has nowhere to drain. It pools behind the ice, and shingles are designed to shed running water, not hold back a puddle. The water backs up underneath them and into the house: wet insulation, stained ceilings, bubbling paint, and mold if it goes on long enough. Often the first you know of it is a drip indoors.

Southern New Hampshire winters are close to ideal for this. A nor'easter leaves heavy snow, a sunny day in the 30s melts some, and the night drops back into the teens. Older capes, colonials and farmhouses with thin attic insulation or finished upper floors tend to get hit hardest.