Roof Ice Dams | Ice Dams

If you live in the cold snowy regions you have seen ice dams on roofs and icicles hanging from the roof eaves.  Typically this thick band of ice forms along the eaves of houses every winter and can cause structural damage. If the damage isn’t structural, it is water-stained ceilings, dislodged roof shingles, sagging gutters, peeling paint, and damaged plaster. All this aggravation is the familiar results of ice dams.

Although there are many ways to treat the symptoms of roof ice dams, but proper air sealing, insulation, and attic venting are the best ways to eliminate the problem. Ice dams form along the roof's edge, usually above the overhang and over the course of a few weeks they become very thick as they migrate up the roof forcing water under the shingles and leaking into the ceiling structure. There is a simple explanation as to why this happens. Heat and warm air leaking from the living space of the home below melt the snow on the roof which trickles down to the colder edge of the roof (above the eaves) and refreezes.  This really keeps more heat in the attic, which in turn makes the roof even warmer and melts more snow causing larger ice dams on the roof. The frigid outdoor temperatures ensure a quick, fast and deep freeze at the eaves. The worst ice dams usually occur when a deep snow is followed by very cold weather.

Damage Caused by Ice Dams:

Contrary to popular belief, gutters do not cause ice dams. However, gutters do help to concentrate ice and water in the very vulnerable area at the edge of the roof. As gutters fill with ice, they often bend and rip away from the house, destroying fascia, fasteners, and downspouts.

The melting ice leaks on attic insulation which caused degradation of the insulation. The wet insulation doesn't work well and because it is compressed it is not as effective after it dries. This sets up a vicious cycle: heat loss-ice dams-roof leaks-insulation damage-more heat loss.

Water often leaks down inside the walls, where it wets wall insulation and causes it to sag, and leaving uninsulated voids at the top of the wall. The moisture gets trapped in the wall cavity between the exterior plywood sheathing and the interior vapor barrier. Soon you can smell the decay as the structural framing members begin to decay or at the very least a buildup of mold and mildew on the surface of the wall. Also the paint will begin to blister and peel.  

Solving the Roof Ice Dam Problem:

1. The way to stop or prevent ice dams from forming is to keep the entire roof cold. This means blocking all air leaks leading to the attic from the living space, increasing the thickness of insulation on the attic floor, and installing a continuous soffit and ridge vent system. Be sure that the air and insulation barrier you create is continuous.

2. The worst of all solutions is shoveling snow and chipping ice from the edge of the roof. People attack mounds of snow and roof ice with hammers, shovels, ice picks, homemade snow rakes, and crowbars. People that practice this method of ice removal believe that if there is no snow or ice then there is no leaking water. Unfortunately this method causes more harm than good.

3. Roof heat tapes or ice melt cables are installed on roofs in northern climates with heavy snowfall. The snow can melt during the day at the roofs peaks and refreeze at night on the eaves. This refreezing causes an ice dam. Water can leak back through a roof if the ice dam is thick enough. Heating cables when installed properly can prevent ice dams from forming on the roof edge. The cables should be U.L.-approved and replaced when they begin to show any sign of wear or are becoming brittle.

4. When installed properly the ice melt cables are run in a zigzag "V" type pattern up and down the roof edge. They are typically run on only the uninsulated eaves of the home. This is the area most prone to ice dams. The cables can also be run in valley areas on the roof. These areas may be prone to freezing due to heavy shade conditions during the winter season. The cables must be attached securely to a shingled roof so they cannot be pulled loose by any movement of the melting ice dam. A single cable should also be run through the horizontal gutter system to keep it free flowing. Another cable should also be run inside all downspouts so ice cannot form there. A free-flow path must be made for the water or else is will freeze and cause damage to the roof and gutter system.

5. A separate GFCI (ground fault circuit interrupter) circuit breakers should be used for the power source of the heating cables. Many of these cables will have wattage ratings which will dictate separate circuits. A circuit rated for 20 amperes should be used for ice melt cables. When installing the cables the wires should not cross or come in physical contact with each other. This may cause the cables to overheat and perhaps causing a fire. Many installations will use outdoor rated electrical receptacles that are installed under the eaves of the roof to power the cable ice melting system. The cables are plugged into the outdoor outlets on a seasonal or as needed basis.

Most ice melt cable systems come with a built in thermostat. These temperature controllers switch the cables on and off as the temperature drops to an ice forming point. Some heating cables come with no form of temperature control, as long as they are plugged into a power source the cable will continue to heat. This type should be monitored and unplugged when the ice is melted.  

If you are having ice dam problems do not ignore them as they must be dealt with before they cause water damage to your home. Installing an ice melt cable system is very effective and an inexpensive way to deal with ice dams.  Ice melt or rock salt is not effective in preventing ice dams.