Shoveling snow off a flat roof is the least expensive method of snow removal. If snow is hard-packed or wet, shoveling is not only arduous work, it's dangerous. Snow is heavy; a square foot of wet snow might weigh over 15 lbs. Considering that a flat roof can measure 500 to 1,000 square feet, that's a lot of weight to lift, even for a fit adult. More importantly, if a flat roof is stressed from the weight of snow and ice, the addition of an adult male could cause roof collapse. Though municipalities such as New York City require homeowners to remove snow and ice from the rooftops, in the long run, it's safer to hire a snow-removal service.
Radiant heating or electric de-icing cables work by melting snow and ice on rooftops and gutters. Snow and ice pack over time can cause ice dams or structural roof damage. According to the Canada Mortgage and Housing Corp., cables should be run from the downspout drain to each corner in a criss-cross pattern. For obstacles such as chimneys, skylights and vents, it should be mounted in a loop. The cost is inexpensive. Based on an energy estimate calculator, if a flat roof measures 1,000 square feet and you use the cables two hours per day, based on an energy cost of $.10/kW, your cost per day would be $1.60 (varies based on energy costs in your region). This energy cost might be more than a shovel, but over time, it's far less expensive than a roof leak or collapse.
Rock salt and calcium chloride effectively melt snow and ice by lowering the freezing point for water. As a method for flat roofs, they can be nearly as corrosive as they are on concrete and asphalt pavements. Magnesium chloride, an alternative ice-melt product, is far less toxic and corrosive. When spread on a flat roof, it melts ice, lightens the stress on a flat roof and channels runoff. While you can fill stockings with magnesium chloride to be laid on the snow and ice after a storm, a preventative option is to spread a layer of magnesium chloride on the roof before a storm.
Professional Roof Cleaning
It's cheaper to clear snow from a flat roof yourself. Because of inherent health risks associated with lifting snow and the stressors affecting a flat roof after a major snow storm, a professional roof-cleaning company is a prudent consideration. Many companies use cherry-picker trucks with baskets that hover above your roof. Professionals can clear snow and can assess potential ice dams and leaks before they occur.