With the heavy snowfall this week, and the weather now getting milder into the weekend, it’s important that people are mindful of the risks associated with heavy snow on roofs as well as its removal.
Please find important safety information from Fire Prevention Officer (FPO) Don Egan.
Roof Safety In Heavy Snow Conditions
A building’s ability to stand up to weight of ice and snow depends on:
• Live and dead load design
• Age of the building and the roof
• Condition of the roof
• Maintenance during or after a major snow storm
Range in Snow/Ice Weight
• The weight of 1 foot of fresh snow ranges from 3 pounds per square foot for light, dry snow to 21 pounds per square foot for wet, heavy snow (Gooch, 1999).
• One inch of ice weighs a little less than 5 pounds per square foot, and 1 foot of ice weighs approximately 57 pounds per square foot. Ice weighs significantly more than heavy, wet snow per inch depth. In part, this is why it is important to prevent ice buildup on a roof structure.
Warning Signs of Overstress Conditions During a Snow Event:
• Overstressed roof deck or framing typically displays some warning signs. Wood and steel structures may show noticeable signs of excessive deflection before failure. The following warning signs are common in wood, metal, and steel constructed buildings:
• Sagging ceiling tiles or boards, ceiling boards falling out of the ceiling grid, and/or sagging sprinkler lines and sprinkler heads
• Sprinkler heads deflecting below suspended ceilings
• Popping, cracking, and creaking noises
• Sagging roof members, including metal decking or plywood sheathing
• Bowing truss bottom chords or web members
• Doors and/or windows that can no longer be opened or closed
• Cracked or split wood members
• Cracks in walls or masonry
• Severe roof leaks
• Excessive accumulation of water at non drainage locations on low slope roof
To avoid roof collapse, snow removal should begin prior to reaching the snow load limit of the roof.
• For safe removal that won’t endanger you or damage your roof, consult a roofing contractor.
• A heavy duty push broom with stiff bristles or roof rake may be used to brush off the snow down the slope of the roof.
• Do not pull snow back against the slope or sideways since the snow may get underneath the cover and can break shingles.
• A snow blower should not be used.
• Keep snow away from building exits, fire escapes, drain downspouts, ventilation openings, and equipment.
• Removing snow completely from a roof surface can result in serious damage to the roof covering and possibly lead to leaks and additional damage. At least 2 inches of snow should be left on the roof.
• If there is any concern that snow loads may cause a collapse of the roof structure, cease all removal activity and evacuate the building.
• Whenever snow is being removed from a roof, be careful of dislodged icicles. An icicle falling from a short height can still cause injury.
• When using a snow rake, be aware that roof snow can slide at any moment. Keep a safe distance away from the eave to remain outside of the sliding range.
• Buried skylights pose a high risk when you are removing snow. Properly mark this hazard as well as other rooftop hazards prior to snow events.
• Fall protection should always be implemented when working on a roof.
• Always have someone below the roof to keep foot traffic away from locations where falling snow or ice could cause injuries.