Whenever we get a large snowfall or a lot of snow over time, homeowners, tenants, and business operators should be alert to the danger posed by heavy snow loads on roofs and recognize warning signs of potential structural weaknesses.
Flat and low-pitched roofs, most often found on industrial buildings, but also used in certain home designs, are at the greatest risk of buckling under heavy snow and ice accumulations.
Often the risks can be mitigated by removing snow from roofs of both commercial buildings and homes, but this can also be dangerous. Here are some considerations for deciding whether snow should be removed, and how to remove it safely.
How much snow is too much?
Here are some guidelines from the Insurance Institute on Business and Home Safety. IBHS estimates the typical roof can handle 20 pounds per square foot of additional weight. However, if you have an older home or older roof, especially if you have had problems before, you might want to figure on less than 20 pounds.
- Fresh snow: 10 to 12 inches of new snow is equal to one inch of water, or about 5 pounds per square foot of roof space, so you could have up to 4 feet of new snow before the typical roof will become stressed.
- Packed snow: 3 to 5 inches of old snow is equal to one inch of water, or about 5 pounds per square foot of roof space, so anything more than 2 feet of old snow could be too much for your roof to handle.
- Ice: one inch of ice equals one foot of fresh snow or 5 pounds per square foot.
As an example, two feet of old snow and two feet of new snow could weigh as much as 60 lbs per square foot of roof space, which is beyond the typical snow load capacity of most roofs.
Removing snow safely
- Consider hiring professionals to do the job. The combination of heights plus ice makes this one of the more dangerous house chores. If you choose to do the task yourself, have someone outside with you to assist -- and to remind you not to take dangerous risks.
- Use a snow rake for pitched roofs (available at most hardware stores) to remove snow from your roof.
- Remember that any snow that comes down can come down on you, so stand well back and rake small amounts at a time.
- Start from the edge and work your way up onto the roof with the rake.
- Try to shave the snow down to 2 or 3 inches on the roof instead of scraping the roof clean, which will risk damage to your shingles or other roof covering.
- An aluminum rake will conduct electricity. Check where the power lines enter your house, and stay well away from that area while using a roof rake.
- Remove large icicles carefully if they're hanging over doorways and walkways. A cubic foot of ice weighs about 62 pounds. Consider knocking down icicles through windows using a broom stick.
- Wear protective headgear and goggles when performing any of these tasks.
- Keep gutters and drains clean, free of ice and snow and keep downspouts clean at ground level.
- If you are a business owner and have employees working on snow removal, review OSHA Winter Safety Guidelines.
Things NOT to do:
As a rule, anything that would require getting on to your roof may be too dangerous for anyone except a professional with the proper training and safety gear.
- SAY NO to climbing on ladders. Ice and snow tend to build up on both the rungs of the ladder and the soles of your boots.
- SAY NO to using an electric heating device like a hair dryer or heat gun to melt snow or ice. Melting ice makes water, and the mixing of water and electricity is a very bad idea.
- SAY NO to using an open-flame device to remove snow and ice. An open flame can damage roofs and gutters and even set your house on fire, definitely going from bad to worse.
Some signs that a roof might be stressed
- Sagging roof sections
- Severe roof leaks
- Cracked or split wood members
- Bends or ripples in supports
- Cracks in walls or masonry
- Sheared off screws from steel frames
- Sprinkler heads that have dropped down below ceiling tiles
- Doors that pop open
- Doors or windows that are difficult to open
- Bowed utility pipes or conduit attached at ceiling
- Creaking, cracking or popping sounds
If any of these signs are observed, evacuate the building immediately and get the building inspected.