Electrical connections should be moisture-proof and outlets installed in dry locations. The branch circuit supplying the cable must have sufficient capacity to carry the heating load, and all metal gutters and downspouts and all metal siding should be properly grounded. If the cables become twisted and overlap there is a danger that the insulation will melt at the overlap, causing a short circuit. Ice should never be allowed to form in the channels because the heat from the cables may not be sufficient to clear large ice dams once they have formed. Summary The formation of ice dams on the eaves of sloping roofs often causes water leakage through roofing composed of overlapping watershedding units.
Snow melting on the roof and freezing at the eaves is the cause of ice damming.
Snow melting is due chiefly to heat loss from the building through the roof or from attic spaces, although some melting can occur from sun radiation. Temporary relief can be obtained from the effects of ice dams by clearing the snow off the roof, particularly at the eaves, and by knocking ice formations from the eaves and valley ends, taking care not to damage the roofing. For a more permanent solution and to limit the formation of dams, consideration must be given to more adequate roof or ceiling insulation, ventilation of air spaces above the insulation, and moderation of inside temperatures. Leakage can usually be avoided by using wide overhangs, wide impervious flashings or roofing at the eaves, or heating cables to melt drainage channels through the ice. Originally published May 1967.