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Ice damming happens when ice forms on the edge of a roof and prevents melting snow from draining off the roof. Water begins to back up behind the dam which can lead to interior leaking resulting in damage to walls, ceilings, insulation, electrical, and other areas.
Ice damming occurs through a complex interaction between, snow cover, outside temperatures, and heat loss from your home and the signs you might have an ice dam problem may begin to show. Snow must be present on the roof coupled with the higher elevation of the roof slope to be above 32 degrees Fahrenheit while the lower portion of the roof slope is below 32 degrees Fahrenheit. Additionally the ambient outside temperature must also be below 32 degrees Fahrenheit and must at minimum be sustained over a period of time.
The snow on the upper portion of the roof begins to melt and as the water cascades down the roof slope and meets the lower section that is 32 degrees or lower it freezes and turns to ice.
This begins the process of forming an ice dam as its fueled with a continues flow of melting snow flowing down the roof slope. As the water freezes it creates a dam that catches water and prevents it from shedding off the roof. The water begins the seep up under the roofing shingles and finds it way into the interior of your home where the damage begins.
Being that most ice dams begin that at the eves or bottom edge of the roof, that is obviously a warming heat source further up the roof slope. This heat source mainly comes from the home itself but in rare instances heat from the sun my also cause roof surface temperatures to be different.
In your home, heat will move through your ceiling and insulation through conduction, not having insulation with a high “R” value per inch contributes to the loss of heat through conduction.
The top portion of the insulation becomes warmer that the surrounding areas inside the attic. Therefore, the air just above the insulation is heated and rises, carrying more heat through convection to the roof. These higher temperatures inside the insulation’s top surface in comparison to the roof’s sheathing transfers heat outwardly by radiation. We can reduce these two modes of transference of the heat by adding more insulation inside the attic. The idea here is to make the temperature in the attic as whole more consistent and even which will directly affect the convection and radiation from the roof sheathing surface inside the attic.
Additional factors that can contribute to ice damming are roof exhaust systems that penetrate the roof surface. Kitchen and or bathroom exhausts that terminate to close to the exterior roof surface can contribute to melting the snow which can begin the ice damming process. Should the exhaust systems be too close to the roof surface they may need to be removed and installed correctly or extended.
Chimneys whose exhaust system is inside the exterior walls of your home can also increase the temperature of attic spaces and any leaky heating air ducts will also increase the ambient temperature inside the attic space as well.
Remove any existing snow from the roof surface with a snow rake and then begin to remove any ice buildup that’s accumulated on the surface of the roof. Do not use and ax or other sharp tool as you’ll risk cutting through the shingles. Use a blunt mallet and tap lightly in order to break up the ice. This is slow and dangerous work, so hire someone experienced at roofing.
Clear out gutters and downspouts. This can also be dangerous work if a ladder is required so we recommend hiring a professional roofing company to do this for you.
You can also use calcium chloride to melt through ice accumulation on your roof but do not use rock salt! Rock salt will damage paint, metals and your roofing system.
One of the first steps in preventing ice dams is to prevent or control the loss of heat from your home and taking steps to ensure that the temperature in your attic space remains the same throughout the whole attic.
Removal of snow from the roof the key ingredient for the formation of ice dams before they can begin.
Attic ventilation is key to ensuring a consistent heat inside that attic therefor ridge and eve ventilation systems are important. These allow for a continuous flow of air to circulate through the attic. There needs to be a minimum of 1 square foot of attic ventilation for every 300 square feet of attic floor space.
Example: If the total square feet of the attic floor space is 900 you’d need 3 square feet of attic ventilation.
If your roof has an electric attic fan its recommended to cap it during the winter months. Have a roofer inspect any metal roof flashing for gaps where heat can be lost and either repair or seal them.
Inspect HVAC duct joints for leaks and seal them with mastic of HVAC tape and cover them with R-5 or R-6 foil faced fiberglass insulation.