It’s imperative that building owners and builders are wary of excessive snow on metal roofs during winter months, especially in snow and ice-prone areas like here in New England. Staying educated on the building’s snow limit and taking action to remove the snow will help prevent damage to the metal building’s structure and safeguard the investment. 

Seasonal snowstorms with heavy snow can create packed layers of snow and ice. Just a few feet of depth may weigh 50 psf (pounds per square feet). Snow drifts can increase loads and provide risk of building damage or collapsing. Various snow types (light, fluffy or heavy, wet) from different geographic areas need to be considered. For example, snow in the western United States is typically lighter and less dense than snow that falls on the East Coast, which is usually heavier and wet. 

Snow on Pitched or Flat Roofs

Flatter roofs are most vulnerable to packed snow that causes heavier roof loads. Snow can accumulate when blowing from a taller building and may drift to a shorter building. Drift loads also take place between close buildings, ridges, in valleys, behind parapets, near rooftop units and on eave canopies or overhangs. A building with a high-pitched roof is preferable and easier to clear ice and snow. 

Environmental aspects may change the original building’s construct and can affect drifting. Perhaps trees have grown-in over the years and affect where wind-blown snow accumulates. Changing the building’s structure post-construction can also cause concern affecting the amount of snow load capacity. 

Roof snow management recommendations for building owners:

• Monitor snow accumulations and depths on metal roofs and clean often, as needed. 
• Keep drains and gutters clear of ice and snow to prevent damaging ice dams.
• Use heat tapes in gutters and downspouts to help prevent ice build-up during average winter temperatures. 

Warning signs of excessive snow accumulation: 

• Deflection of purlins.
• Popping of ceiling tiles in dropped ceilings.
• Strange noises from any part of the metal building.

What is snow load?

When snow and ice accumulate, the downward force that weight creates on the building’s roof is the snow load. If built in a snow/ice-prone area, even well-designed and constructed buildings in good condition can fail if the snow load exceeds the weight it was designed to manage. 

How to calculate snow load: 

Multiply the depth of snow in feet by the weight of a cubic foot of snow. For example, the snow weighs 10 pounds per cub foot and there are 1.5 feet on the roof, each square foot of the roof is getting approximately 15 pounds of pressure. 

How to remove snow and ice from metal roofs:

Be safe.

• When working on the roof, ensure all proper safety precautions are being implemented.
• Always work in pairs.
  Work from the gable end of the building so sliding snow doesn’t slip off.

Follow the order.

• Remove drifted snow first.
• Ensure the level of remaining snow is even.
• Starting with the most snow-packed bay, remove snow from the middle 1/3 of each bay, from eave-to-eave.
  Finish removing snow from the rest of the building.
• Tip: Gabled buildings should have snow removed on both sides of the ridge at the same time.

Keep it balanced.

• When removing snow, ensure the roof load is not unbalanced.
• Keep the snow depth differences at a minimum across the roof.
• Slowly remove snow in layers across the entire roof.
• Careful removal.
  Remove all hanging icicles from gutters and eaves, as they add significant weight and cause backups of snow and ice.
• Cautiously remove the snow from the eave towards the ridge, and carefully ensuring snow or ice doesn’t break away to slide down the roof.