Salt Vs. Calcium Chloride to Melt Ice on Roof

Sodium Chloride

• Homeowners, businesses and municipalities commonly use sodium chloride, or rock salt, to melt ice on walkways, stairs and streets. Because of its highly corrosive nature, most ice removal and roofing experts recommend against using salt to melt ice off of roofs. Sodium chloride contains oxidizing agents that can accelerate rust and corrode roofing materials. It can also shorten the lifespan of metal gutters, downspouts and flashings, according to State Farm Insurance. Additionally, the runoff from a liberal application of salt can damage or kill grass and other plantings close to the building. Salt runoff also can damage or discolor exterior brick walls and aluminum siding.

Calcium Chloride

• Calcium chloride is a high-performance deicer. Like sodium chloride, it’s exothermic, meaning it melts ice by releasing heat. Although sodium chloride is effective down to about 20 degrees Fahrenheit, calcium chloride still works at temperatures below 0 degrees. The website This Old House suggests filling the leg of discarded pantyhose with calcium chloride and positioning it over the ice dam so that it hangs slightly off the edge of the gutter. As the chemical melts the ice, it creates a channel to release any water trapped against the roof. Most experts, however, do not recommend using calcium chloride on roofs. Like sodium chloride, calcium chloride contains oxidizing agents that can corrode or damage roofing, siding, gutters and plants.

Ice Dam Removal

• Making drainage paths through the ice that sits along the lower edge of a sloped roof allows the runoff of trapped water. You must first expose the ice by clearing away any loose snow. If outdoor power outlets are available, the Canada Mortgage and Housing Corporation recommends using electrical roof deicing cables to heat and melt the ice. By attaching loops of electric deicing cables to a long board positioned just above the roof’s edge, you can create several channels for water runoff. If you don’t have outdoor power, use a non-corrosive deicer such as calcium magnesium acetate, urea, potassium chloride or ammonium sulfate. Such chemicals are less effective than more corrosive deicers, but are much less likely to damage your roof, gutters, siding and nearby landscaping.

Considerations

• Clearing ice dams can damage your roof more than the ice itself. While corrosive chemicals such as sodium chloride and calcium chloride can harm your roof, gutters and siding, chipping away at ice with a sledgehammer or pick can take chunks out of your roof. If you can’t discern whether or not the ice on your roof is causing structural damage, consult a professional. Likewise, if you don’t have the equipment, help and physical ability necessary to safely remove roof ice, call a professional. Ice dam removal can be a dangerous, slippery job. Melting or removing ice near the edge of a roof can release higher sections of ice that could slide down and hit you as you work.