Snow Load and Your Roof: What North Idaho Homeowners Need to Know

What Roof Is Best for Heavy Snow in Idaho?

A steep roof built for your area's required snow load, with a material that sheds snow and a cold, well-ventilated attic. Standing seam metal sheds snow well, and the trusses and rafters carry the weight, so the structure matters as much as the roofing.

• Pitch: steeper roofs shed snow better. Coeur d'Alene's building department notes that roofs flatter than 3/12 tend to hold more snow moisture
• Material: standing seam metal lets snow slide off, so plan on snow guards over doors and walkways. Architectural shingles also handle snow well when the structure and ventilation are right
• Structure: the trusses and rafters carry the snow's weight, and they need to be sized for the snow load your county or city requires
• Ventilation: a cold, well-ventilated attic reduces ice dams, which hold extra snow and water on the roof

Comparing materials? See our North Idaho roofing materials guide, when to switch to a metal roof, and snow guards explained.

What Are the Roof Snow Load Requirements in Kootenai County?

There's no single roof weight limit for Idaho. Kootenai County and each city set the snow load new homes must be designed for: 40 to 60 pounds per square foot in the county depending on the zone, 40 in Coeur d'Alene and Post Falls, and 40 or 50 in Hayden.

Roof snow loads run lower than ground snow loads because roofs don't hold snow the way flat ground does. Hayden bases its design loads on the University of Idaho's Ground and Roof Snow Loads for Idaho. Rathdrum and other cities set their own values, so check with your building department for your address.

How Much Snow Can a Roof Handle?

It depends on the snow load the roof was designed for and how wet the snow is. Using Coeur d'Alene's rule of thumb of about 1.25 pounds per square foot per inch, a 40 psf roof holds roughly 32 inches of average snow, and less if it's wet or icy.

1.25 psf

Per inch of snow on the roof

5.2 psf

Per inch of ice

20 lb/cu ft

Saturated snow

Snow can weigh anywhere from about 1 pound per cubic foot to over 21, depending on its moisture, so the same depth can put very different loads on your roof. By the city's example, 20 inches of snow is about 25 psf, under a 40 psf design load. Add 5.2 psf for each inch of ice.

To check your own roof, Coeur d'Alene suggests cutting a 1 foot by 1 foot square of snow, the full depth, and weighing it in a plastic bag. That weight in pounds is the load per square foot.

When Does Snow Become a Problem?

Snow becomes a problem when it piles up without melting, when rain soaks into it, when wind drifts it into one spot, or when ice dams hold it on the roof.

What Are the Warning Signs of Snow Overload?

A sagging ceiling, sharp cracking or popping sounds, doors or windows that suddenly stick, a dip in the roof's ridge line, and new leaks during heavy snow are all signs the roof is under too much load.

• Sagging ceiling: the most urgent sign. Leave the area under it and call a professional
• Sharp cracking or popping sounds, especially with visible movement
• Doors or windows that suddenly stick or won't latch
• A dip or bow in the ridge line when you look at the roof from the street
• New leaks during a heavy snow, not after a thaw

Should You Remove Snow From Your Roof?

Usually not. Most roofs handle a normal storm. Consider removing snow when accumulation gets close to your roof's design load, when heavy rain is forecast on top of deep snow, or when you see warning signs, and do it from the ground.

Coeur d'Alene's building department warns about the dangers of shoveling or raking a roof: damage to roofing, sliding off the roof, falling from a ladder, overexertion, and snow sliding onto you. The city leaves the decision to each property owner.

How Does a Well-Built Roof Handle Snow?

Through framing sized for the local snow load, solid decking and connections, enough pitch to shed snow, and an attic ventilated to stay cold.

• Framing: trusses and rafters sized for the snow load your building permit requires
• Deck and connections: proper nailing, adequate sheathing, and correct truss connections
• Pitch: steeper roofs shed snow more readily than low-slope roofs
• Ventilation: a cold attic reduces ice dams. See our roof ventilation guide

If you're worried about an older roof, an Idaho licensed engineer can tell you what it's designed to carry. A roof inspection before winter checks the roof, flashing, and ventilation.