Snow on a Flat Roof: Loads and Safe Removal in Omaha

Because nothing moves it. A pitched roof sheds some of its snow as it melts and slides; a flat or low slope roof holds what lands on it, and the wind piles more against parapets, walls, rooftop units and any higher roof next to it. OSHA notes that a roof's snow load depends on drifting, melting and freezing again, the roof's slope and type and its design features, not just the snow on the ground.

Wet snow makes it worse. FEMA's figures, quoted by the Department of Energy, put a foot of heavy, wet snow at about 21 pounds per square foot (psf), against about 3 psf for a foot of light, dry snow.

Whatever its engineer designed it for under Omaha's building code (the 2018 International Building Code as the city adopted it). Section 1608.1 says design snow loads are determined by Chapter 7 of ASCE 7, the national standard for design loads on buildings, and Section 1603.1.3 says the building's construction documents must show the ground snow load, with the flat roof snow load and drift details where the ground snow load is over 10 psf.

So the place to find a building's number is its structural drawings. For comparison, Omaha's residential code uses a 25 psf ground snow load for houses (how much snow a roof can hold).

OSHA's hazard alert for rooftop snow removal sets out the order:

1. Know the load before anyone goes up. Confirm the roof can carry the workers and their equipment on top of the snow, using the building's design load.
2. Find what the snow hides. OSHA lists skylights, roof drains and vents among the hazards to mark before work starts.
3. Use fall protection. OSHA requires it for workers at heights of 4 feet or more in general industry and 6 feet or more in construction.
4. Remove snow evenly, and do not pile it on the roof, which concentrates the load on one part of it.
5. Protect people below from snow and ice coming off the edge.

The alert's first advice still applies on a flat roof: clear what you can without people on it.

The same ones as on a house, at a larger scale. FEMA's guidance, quoted by the Department of Energy, lists sagging or visibly bowed roof framing or ceiling panels, creaking or cracking sounds, doors or windows that will not open or close, and cracks in walls, ceilings, framing or masonry. OSHA adds that anyone near a snow loaded roof should stay alert to unexpected sounds or movement, because it could collapse.

If you see a sign, clear the space under it and call a structural engineer. The warning signs guide goes through each one.

That depends on the building more than the brand: its slope, its drains and how it is used. The flat roof options guide compares TPO, EPDM and PVC for Nebraska buildings, and Rocket Roofing General Contractor installs and repairs all three through commercial roofing.

After a heavy winter, have the roof checked for seams, flashing and drains the snow and ice worked on. The inspection is free, with a free estimate in writing.

Against anything that stops the wind. Drifts build against parapets, rooftop units, penthouses and any higher roof beside a lower one, and OSHA notes that drifting is one of the factors that make a roof's load differ from the snow on the ground. A lower roof next to a taller building can carry far more than the open middle of the same roof. Clearing usually starts where the drifts are.

Enough to matter. OSHA tells employers to evaluate the loads on a roof, meaning the total weight of the snow, the workers and the equipment they use, against the roof's load limit before anybody goes up, and to stay alert to unexpected sounds or movement because a surface weighed down by snow, or by water from melted snow, could collapse. A snow blower, a pile of cleared snow or four people standing together put weight where the design did not expect it.

Sometimes, with their own rules. OSHA's hazard alert notes that aerial lifts are sometimes used to reach roofs and apply de-icing materials, and says operators must be trained, the equipment kept and run by the maker's instructions, and safety devices never overridden. Lifts bring their own electrical hazard near power lines, which the same alert covers.

Where nobody is. OSHA's planning questions include how people on the ground will be protected from snow and ice falling off the roof. On a commercial building that means closing the walks and entrances under the work, and keeping the cleared snow away from drains, doors and anything it could bury.

Rocket Roofing General Contractor has served Omaha, Papillion and the rest of Nebraska since 2008. We are registered with the Nebraska Department of Labor, NE DOL #98741-26, and we are a GAF Certified Residential Roofing Contractor. Our crews physically clear snow and ice from roofs and steam ice dams. Headquarters: 5634 S 85th Cir Ste 204, Omaha, NE 68127. Call us at (402) 291-8888.