Rock Salt on Roof Shingles

Rock Salt

• Rock salt, or sodium chloride, is simply table salt, with larger crystals and an additive included to prevent clumping. It's used as a deicing agent because of its effectiveness at melting snow and ice between the temperatures of 16 and 20 degrees F. It's also widely available and usually one of the least expensive deicing products.

Roof Applications

• Deicing agents are used on roof shingles to melt ice blocks, particularly if there is an ice jam. The jams form when melting snow flows down the roof shingles to an area of the roof that is below 32 degrees F -- often due to poor insulation -- and the cold temperature causes the water to refreeze. The ice block prevents additional melting snow from flowing off of the roof, backing up the water, often into the home's ceilings and walls. Deicing products are used to melt the ice block, but since they can cause damage to the roofing materials, they should be used sparingly.

Using Rock Salt

• Rock salt is not recommended as a proper deicer to use on roof shingles. It's corrosive and can damage not only the shingles, but also other roof materials, siding, downspouts and gutters. Rock salt releases chloride ions, which are toxic and can pollute lakes, rivers and other waterways as well as kill plants and trees or affect their growth.

Other Options

• Magnesium chloride or deicing products marketed as "pet-safe" are recommended for use on roofs. They are much less corrosive and are environmentally friendly. To maintain the mess that these pellets can create on roof shingles, fill one leg of a pantyhose or a sock with the product and place it on top of the ice block. Another method that prevents the deicer from sitting on the roof is to break holes into the top of the ice block every few feet along the gutter. Fill the hole with the deicing product and both the deicer and water will flow down the gutters.