SYRACUSE ROOFING COMPANY

You may be tempted to climb up on your roof and shovel off all that snow that’s been building up this winter. But don’t. It’s dangerous, and you may cause more damage than the snow will. That’s the advice we got when we asked Eric Lui, a professor of structural engineering and mechanics at Syracuse University, if it’s a good idea to remove snow from roofs. Lui said a roof built according to state building codes should be able to withstand the weight of any snow that could accumulate on it.

“Never climb up on the roof,” Lui said. “It’s too dangerous.”

He said building codes in New York require that roofs be able to withstand a snow load of at least 25 to 35 pounds per square foot, depending on the pitch of the roof. Clearing snow like this from roofs may actually cause more damage to the roof than the snow will.

On average, that’s a requirement that roofs be able to withstand 30 pounds per square foot of weight from snow. That’s the equivalent of three feet of fresh snow, or one foot of packed snow, Lui said. That’s the most you’re likely to see accumulate on a pitched roof because any more than that will likely slide off, he said.

(If you’re wondering about the math, here it is: Fresh snow weighs one-sixth as much as the equivalent volume of water, and packed snow weighs half as much as the same volume of water. A cubic foot of water weighs 62 pounds. One-sixth of that is approximately 10 pounds, so three square feet of fresh snow weighs 30 pounds. One-half of 62 pounds is approximately 30 pounds, so one square foot of packed snow weighs 30 pounds.)

Lui said a person walking on a roof would be putting far more weight per square foot on the roof than any likely snow load. (A 200-pound man standing on a roof, for instance, would be putting 200 pounds per square foot of weight on the roof. That’s 170 pounds more than any likely snow load on that same spot.)

So getting up on a roof to clear it of snow would actually be increasing the odds of a roof failure, Lui said. And if you can walk on the roof without falling through, that’s proof that it’s strong enough to withstand the snow load, he said.

Not only that, but Lui notes that it’s risky to be walking on a roof full of snow. Two people died in separate incidents in the suburban Boston town of Canton this week when they fell from roofs while clearing snow.

Lui also advises against clearing snow from the edge of roofs to prevent ice dams, which can lead to roof leaks. Ice dams should not form on properly insulated roofs, he said.

He does, however, recommend knocking off icicles that hang above where people walk, such as doorways. People can be injured or even killed if hit in the head by a falling icicle, he said.