How to prevent break ice dams

Preventing leak damage caused by melting roof ice. Snow melting on a roof refreezes on cold overhangs, creating ice dams; these dams trap water that may eventually leak into the house. The permanent way to prevent ice dams is to properly insulate and ventilate your attic. These measures will, in addition, save on heating and electric bills.

A temporary stopgap is to install electric-heat cable bought in a kit. For a roof overhang of 1 foot, you’ll need enough cable to run roughly 21/2 times the length of your roof, plus the length of the gutters and downspout.

Fix the kit’s aluminum clips or clamps to the shingles, following the directions given in the kit, and secure the cable in a zigzag pattern. The correct distance between peaks of the zigzag depends on the amount of local snowfall: space them 11/z feet apart in average snowfall areas and 1 foot apart in snowbelt areas.

Run cable through the gutters and the downspout. To reduce heat loss, keep the cable off the bottoms of the gutters by clamping it to the gutter hangers. Don’t let sections of cable touch each other.

Plug the cable into the receptacle of an outdoor waterproof outlet box or bring the cord through a window and plug it inside. Turn it on when snow falls and leave it on while snow stays on the roof. Some cables have a thermostat that turns on the power when the temperature nears freezing.