Ice dams on roofs damage thousands of homes every winter. They are caused when warm air in the attic melts the underside of the snow on the roof. That's usually because of inadequate insulation and airflow in the attic. The water from the melted snow then sheds toward the eaves. The temperature at the eaves is much lower, however, and as a result, the water refreezes at the roof's edges. As the water refreezes, ice dams begin to form on the roof. The ice dams can become very thick, from several inches to even a foot. Once ice dams form, additional water from melting snow on the roof can begin to back up underneath the lower shingles. Eventually, the water finds its way into the home, onto ceiling edges and inside surfaces of exterior walls. Dark spots form on the ceilings, and wall paint begins to bulge with trapped water. In addition, puddles begin forming on the floor.
The best way to prevent ice dams on a roof starts back during the construction of the home. A roofing underlayment, such as Grace's Ice & Water Shield, should be installed along the roof edges and valleys before the installation of the shingles.
In addition, the homebuilder can increase the heel height of the roof rafters or truss over the exterior walls. By increasing the heel height, more space is available in the attic near the eaves for supporting additional insulation without restricting airflow from the soffit vents.
Also, the builder can extend the roof rafter or truss tails farther out from the exterior walls of the home so that any water that may get under the shingles will simply drip out the bottom soffit areas and not get into the home.
Moreover, the homebuilder can make sure there is sufficient attic insulation and ventilation so that the attic temperature stays nearly as cold as the outside air. The colder the attic the less likely snow will melt and form ice dams on the roof.
Although these construction recommendations for preventing ice dams on roofs are great Monday morning quarterback suggestions, they offer little help for those who currently are dealing with roof ice dams. If ice dams already exist on your roof, you have limited options, and climbing up on your roof and hammering them off is not one of them. If you were to chip the ice dams, you might punch a hole through the shingles, cause them to tear and remove some of the aggregate from the shingles.
Your best solution for removing ice dams is to fill long tubular socks or nylon stockings with 3 to 4 pounds of a nonstaining and noncorrosive ice melt product. Place them over the ice dams and up the roofline, effectively running the stockings perpendicular to the ice dams. The socks hold in the ice melt so that it doesn't run off too quickly from the roof. As the socks become soaked, the meltwater becomes saturated with the ice melt. As the ice melt-saturated water drains from the roof, it melts channels into the ice dams, allowing the water to drain more easily from the roof. Place a stocking every few feet along the roofline to create a number of drainage channels in the ice dams. If you have gutters, position the socks so that they extend over them.
Before applying the ice/snow melt socks onto the ice dams, you may want to remove some of the snow near the roof's edge so that you can place the socks in direct contact with the ice dams. Use a snow rake or a snow shovel to do this.
Note that working on ladders that are in direct contact with ice dams and non-stable surfaces is extremely dangerous. Make sure that the ladder is well-anchored to the ground and that it is leaning at an angle that is sufficient enough to prevent it from kicking out on you or laterally sliding. You may want to call in a second pair of hands to help keep the ladder stable while you work on it.
As an alternative to the ice melt-filled sock approach -- and to avoid climbing ladders -- you may want to look for roof melt tablets, which can be tossed from the ground onto the roof. They work similarly to the ice melt sock approach for removing ice dams on roofs by melting drainage channels into the ice dams.
Mark J. Donovan's website is http://www.HomeAdditionPlus.com.