How Much Snow Can a Roof Hold?

It depends on how much water is in it. FEMA's snow load guide puts a foot of light, dry snow at about 3 psf and a foot of heavy, wet snow at about 21 psf, seven times as much. The Insurance Institute for Business and Home Safety (IBHS) measures it by water: 10 to 12 inches of new snow, or 3 to 5 inches of old snow, each hold about an inch of water and weigh about 5 psf.

The Department of Energy's Building America Solution Center quotes both, and the table below lines them up.

By the IBHS figures, a sound residential roof should handle about 20 psf before it is stressed, unless the structure is already damaged or decayed. At about 5 psf for every 10 to 12 inches of new snow, that is roughly 4 feet of fresh snow. Old, packed snow weighs the same 5 psf for every 3 to 5 inches, so the IBHS says more than 2 feet of it may be too much.

Storms stack. Two feet of old snow with two feet of new on top can weigh as much as 60 psf, three times what most roofs are comfortable carrying. That is why the depth alone does not answer the question: what matters is how wet and how packed the snow is, and whether there is ice in it.

Omaha's residential code (the 2018 International Residential Code, as the city adopted it) sets a ground snow load of 25 psf in its climate table, Table R301.2(1). The same table gives a winter design temperature of minus 3 degrees F and marks ice barrier underlayment as required, which its note reserves for places with a history of local damage from ice damming.

Other towns write their own tables. Lincoln amends the same table in its municipal code (Section 20.12.140), and Pottawattamie County, Iowa, lists a 30 psf ground snow load for the parts of the county it permits. Commercial buildings follow Omaha's building code instead, which sends the design snow load to Chapter 7 of ASCE 7; our flat roof snow guide covers those.

Not quite. OSHA notes that the snow load on the ground is only a rough guide to the load on a roof, because melting and freezing again, drifting, the roof's slope, the type of roof and its design features all change what the roof actually carries.

In practice that means the load gathers in places: drifts against a wall or a higher roof, valleys where two slopes meet, and the eaves where ice builds. Snow cleared unevenly can do the same, which is why OSHA says to take it off evenly and not to pile it on the roof.

NOAA's 1991 to 2020 normals put Omaha's snowfall at Eppley Airfield at 27.1 inches a year: 5.8 inches in December, 7.2 in January, 7.8 in February and 3.0 in March. Lincoln's airport averages 26.0 inches, with February its snowiest month at 7.1.

The metro is not even. NOAA's Gretna 4NE station averages 36.4 inches and its Valley station 31.8, so the same storm can leave very different roofs across a few towns. A normal is an average, too: one heavy, wet storm can put more weight on a roof than a month of light snow.

When it is heavy, when storms have stacked, or when the building shows strain: a sagging ceiling, cracking sounds, or doors and windows that stop closing. The warning signs guide says what each means and what to do.

Rake what you can reach from the ground (roof rake guide), and leave the rest to a crew: OSHA says falls cause most of the deaths and serious injuries in rooftop snow removal. Rocket Roofing General Contractor offers roof snow removal, and steams ice dams off the eaves.

Heavier than any snow. The Insurance Institute for Business and Home Safety says an inch of ice weighs about as much as a foot of fresh snow, and the Department of Energy's snow load guide puts a foot of ice at about 57 pounds per square foot and an inch of it at about 5.

That is why a roof with ice along its eaves deserves attention even when the snow on it looks light. The ice gathers where the melt refreezes, at the cold edge over the overhang, and it holds back the next melt as well: an ice dam is weight and a leak at the same time.

Not necessarily. Each jurisdiction fills in its own climate table. Omaha's residential code uses 25 psf. Lincoln amends the same table in Section 20.12.140 of its municipal code, so its value is Lincoln's own; read the section or ask the City of Lincoln's Building and Safety department for the current number.

Across the river, Pottawattamie County's Building Safety Division lists a ground snow load of 30 psf and a winter design temperature of minus 5 degrees F under the State of Iowa building codes it maintains, the 2015 International Residential Code among them. Inside Council Bluffs, the city's own values apply. The town pages for Lincoln and Council Bluffs cover each.

It can. The IBHS figure of about 20 psf for a residential roof assumes a structure that is not damaged or decayed, so an old leak, a soft spot in the deck or framing that has been cut or weakened all lower what a roof can safely carry. Age alone does not decide it; condition does.

Omaha's housing is older than most of the metro's. The Census Bureau's American Community Survey (2019 to 2023 five-year estimates) puts the median year Omaha's housing was built at 1972, with about 18 percent built before 1940 and about 62 percent before 1980. A roof on a house that age may be its first replacement or its fourth, which is what an inspection finds out.

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.