Fluffy, fresh snow can weigh as little as three pounds per square foot compared with 21 pounds for wet, heavy snow, according to FEMA. Ice weighs more: 57 pounds a square foot. Considering the average-size roof in the United States is in the range of 2,000 square feet, the weight of snow and ice can add up to dangerous sums.
Before embarking on a potentially risky mission of removing snow from your roof, determine whether it's necessary. For example, homes built before 1975 may not be structurally sound enough to handle the amount and types of snow being dumped across the U.S. this winter.
Already, dozens of roofs have collapsed in Boston — 44 in just a two-day period. Structural engineer Todd Fratzel told The Boston Globe it's a good idea to remove snow that's 18 inches or more on low-pitch roofs.
But that advice should be taken with caution.
"More often than not, attempting to remove snow from a roof is more hazardous than beneficial, posing a risk to both (people) and the roofing structure," the Federal Emergency Management Agency warned recently.
FEMA says there are many factors that go into "snow-induced structural failures," including a roof's shape, slope, construction, maintenance, exposure to wind, and the type of snow that has accumulated.
