Snow accumulation on flat roofs can pose a safety problem, as the weight of the snow can exceed the safe carrying capacity of the roof. Water accumulated as snow melts can also cause leaks. Hand-shoveling snow off the roof is one of the few options available if the snow load on a flat roof reaches an unacceptable level.
Flat Roof Snow Removal
Building codes in snow-prone areas usually require roof construction capable of handling a considerable snow load. Building owners or managers should know the pounds per square foot the roof is capable of carrying safely.
The weight of snow varies with the water content. In some areas snow is relatively dry and light. Other areas receive snow that is wet and heavy when it falls. The snow will also vary as winter progresses. Early fall and late spring snowstorms often contain more moisture and heavier snow.
Gather 1 cubic foot of snow, melt it and weigh the water. If the water in 1 cubic foot of snow weighs 3 pounds, for example, and there is an average snow depth on the roof of 2 feet, the average load on the roof is 6 pounds per square foot.
On some roofs deeper snow accumulations occur in obstructed areas such as around plumbing vents or heating or air-conditioning units. If the average weight of a cubic foot of snow is 3 pounds and the snow is 6 feet deep in one area of the roof, the load on that area is 18 pounds per square foot. If the roof has a safe load of 15 pounds per square foot, for example, the snow would need to be removed from that area.
Few mechanized options exist for removing snow from a roof. Even if tractors or other snow-moving equipment could be placed on the roof it would likely exceed the safe load-carrying capacity of the roof. Shovels and walk-behind snow blowers can usually be used safely. However, if the roof is at or near capacity from the snow load, workers should be cautioned to spread out to avoid concentrating additional weight in one spot of the roof.