How much snow is too much snow on your roof?

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.

To prevent a roof collapse and remain safe in the process, the Insurance Institute for Business & Home Safety recommends homeowners take four steps:

1. Figure how much weight your roof can support. Most roofs can withstand 20 pounds per square foot of snow.

2. Calculate the weight of the snow on your roof. Ten inches of fresh snow equates to about five pounds per square foot, which means your roof likely can support four feet of fresh snow. Packed snow, however, weighs more: two feet or more of old snow is enough to exceed weight limits. Old snow and new snow combined can easily exceed load capacity. Just two feet of each could collapse a roof. And don’t forget to add ice to the equation. An inch of ice is equal to the weight of a foot of fresh snow.

3. Remove excess snow and ice. That means clearing amounts above 20 pounds per square foot. A snow rake with a long extension arm is recommended. Alternatively, hire a professional contractor to remove the snow and ice for you.

4. Look for signs of a stressed roof. Sagging ceiling tiles, sprinkler lines, popping or creaking noises, jammed doors and windows, cracked walls or a leaking roof are all signs of an overstressed roof.

If your roof is damaged and looks like it’s in danger of collapse, do not risk staying inside or attempt to clean it. Evacuate the premises and contact a structural engineer to assess the problem.

Different regions typically produce different types of snow. Western regions often produce lighter, fluffy snow (that powder skiers and snowboarders rave about), whereas Eastern regions often accumulate heavier snow. Even within regions different snow type accumulate: Boston snow may be different than Worcester snow.

Know your snow and don’t take chances removing it if it’s unnecessary. A final point to remember: It isn’t wise to remove all the snow on your roof as it can cause damage to tiles and start leaks. At least 2 inches of snow should remain on your roof.