Contributing to this formation is warm air that leaks into an unheated attic that creates warm areas on a roof. That in turn causes snow there to melt and then refreeze on a cold overhang. This ice builds up along the eaves and forms a dam.
"Eventually this dam forces the water to back up under the shingles and sometimes into the ceiling or wall inside the home," said Schultheis.
Besides dislodged roof shingles, sagging gutters, damaged insulation and adding water stains on interior ceilings and walls, water from ice dams may cause structural framing members to decay, metal fasteners to corrode and mold and mildew to form in attics and on interior walls.
Schultheis says that it is a good idea to increase the ceiling and roof insulation in the home to R-38 and plug gaps around plumbing vents, wiring, recessed lights and chimneys.
"Keep the attic cold by providing at least two square feet of attic vent for each 150 square feet of attic area. Where the roof rafters meet the walls at the eaves, provide a one inch clearance between the roof sheathing and the ceiling insulation to allow ventilation," Schultheis said.