Cut pantyhose legs off with scissors, trimming the nylon at thigh level to make long tubes.
Pour or scoop the salt or de-icer into the pantyhose legs. Fill to the desired level, leaving at least several inches at the top unfilled. Tie off the top of the pantyhose to seal the salt or deicer in the nylons.
Position the ladder against the house so that it does not wobble or slip on ice or snow; if necessary, place a rug or mat beneath it to provide a safer gripping surface.
Remove as much snow as possible from the affected area of the roof with a snow rake or broom; this should be somewhat easy if the snow is light and has not crusted over.
Climb the ladder carefully and position yourself near the ice dam. Place a salt or deicer-filled nylon across the ice; it will need to run across the ice dam and down toward the lower edge of the roof to create a water channel as the ice melts. Place several of these across the affected area.