Idaho · Weather and your roof

Idaho weather and your roof

An Idaho roof takes spring and summer hail, snow loads that climb from 14 psf in the Treasure Valley to 157 psf in McCall, months of freeze–thaw, wildfire embers and long, hot summers. Here is what each does to a roof, with the sources, and what an Interlock® aluminum roof does about it.

Reviewed by Scott Plumptree, Director of Marketing, The Interlock Group · Updated October 8, 2026

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Hail

June 26, 2026

Several inches of small hail in northwest Meridian.

Snow load

15 psf Boise · 157 psf McCall

Ground snow load, University of Idaho 2015.

Wildfire

Roof = most vulnerable

Ready, Set, Go! Idaho guide.

Hail

Hail in southwest Idaho comes with spring and summer thunderstorms. On June 26, 2026 a storm hit the Boise area with lightning, heavy rain and hail; workers in northwest Meridian reported several inches of small hail on the ground, and the lead meteorologist at the National Weather Service's Boise office said, "It was small hail, but there was an awful lot of it." The meltwater and more than an inch of rain contributed to flooding in some neighborhoods.

What to look for in a roof: an impact rating on the exact product, tested to UL 2218, where Class 4 is the top class. Interlock's Slate, Cedar Shingle, Shake and Mediterranean Tile profiles carry UL 2218 Class 4, verified by Intertek for Delta Building Products. Large hail can still dent aluminum. The Guardian material warranty covers splitting, cracking and perforation from hailstones 1.5 inches in diameter or less; cosmetic dents are not covered. Records of hail reports by county are kept in NOAA's Storm Events Database.

Snow load: valley and mountain

Ground snow load is the weight of snow a building has to be designed for, in pounds per square foot. In Idaho it changes sharply with elevation. The University of Idaho's 2015 study found snow varies so much between Idaho's valleys, plains and mountains that a simple elevation rule isn't enough, and published loads city by city.

2015 ground snow loads for southwest Idaho cities (University of Idaho)
CityGround snow loadElevation listed
Kuna14 psf—
Boise15 psf2,681 ft
Garden City15 psf—
Nampa15 psf2,517 ft
Meridian16 psf—
Eagle17 psf—
Caldwell18 psf2,376 ft
McCall157 psf5,012 ft

Source: Al Hatailah, Godfrey, Nielsen and Sack, Ground Snow Loads for Idaho, 2015 Edition, University of Idaho Department of Civil Engineering. Roof design loads are calculated from these by the engineer or building official; your building department sets the value for your address.

Freeze–thaw

Valley winters bring runs of freezing nights and sunny afternoons. Water that gets into wood, behind a curled asphalt tab or into a cracked tile freezes, expands and widens the opening each cycle. Ice dams form when attic heat melts snow on the upper roof and it refreezes at the cold eave.

Aluminum absorbs no water and can't rot or split, and interlocked panels have no tabs to lift. No roof covering prevents ice dams on its own: they come from heat loss and ventilation, and ice damming is a stated exclusion of the Guardian material warranty. We look at attic insulation and ventilation with you at the estimate, and plan snow guards where a slide would land on people, decks or cars.

Wildfire embers

Idaho's Ready, Set, Go! guide, published by the Idaho Department of Lands: "Your roof is the most vulnerable part of your home because it can easily catch fire from windblown embers." The guide names roof valleys, open ends of barrel tiles and rain gutters as points of entry, and vents in eaves and cornices as particularly vulnerable.

Boise writes it into its fire code: in the city's wildland-urban interface areas, ignition-resistant construction calls for a Class A roof assembly or covering, including when a roof is replaced (Boise City Code 5-12-53). Aluminum does not ignite, and an Interlock® roof is Class A Fire Rated Available, as a complete assembly.

Summer sun and heat

Southwest Idaho summers are long, hot, dry and bright. Heat and ultraviolet light age asphalt and dry out wood. The Alunar® finish on an Interlock roof uses pigments that reflect much of the sun's near-infrared energy, in every color, and carries a 30 Year Alunar® Coating Warranty.

Building codes in Idaho

According to the Division of Occupational and Professional Licenses, Idaho's adopted residential code is the 2018 International Residential Code with Idaho amendments, called the Idaho Residential Code (2020 Edition); the 2018 International Building Code and 2018 International Energy Conservation Code apply with amendments, and the State Fire Marshal administers the 2018 International Fire Code. Cities enforce the codes through their building permits: Boise, Meridian and Nampa all require a permit to re-roof.

Questions, answered

Does Idaho get hail?

Yes. Hail in southwest Idaho comes with spring and summer thunderstorms. On June 26, 2026 a storm left several inches of small hail on the ground in northwest Meridian, according to East Idaho News, which quoted the National Weather Service's Boise office.

What is the best roof for hail in Idaho?

Look for a UL 2218 Class 4 impact rating on the exact product. Interlock's Slate, Cedar Shingle, Shake and Mediterranean Tile profiles carry UL 2218 Class 4, verified by Intertek for Delta Building Products. Any metal roof can still take cosmetic dents from large hail.

What is the snow load in Boise?

The University of Idaho's 2015 ground snow load study lists 15 psf for Boise, 15 psf for Nampa, 18 psf for Caldwell and 157 psf for McCall. Your building department sets the design load for your address.

Is a metal roof good for snow?

Metal sheds snow and absorbs no water, so freeze–thaw has nothing to split. Plan snow guards where a slide would land on people, decks or cars. Aluminum panels are light, about 0.41 to 0.59 lb per square foot installed (ICC-ES ESR-1790), so they add little to what the structure carries.

Does a metal roof prevent ice dams?

No roof prevents ice dams on its own. They come from attic heat loss and ventilation, and ice damming is a stated exclusion of the Guardian material warranty. We look at insulation and ventilation with you at the estimate.

What roof is best for wildfire in Idaho?

A non-combustible covering on a Class A rated assembly, with gutters kept clear and vents screened. Idaho's Ready, Set, Go! guide calls the roof the most vulnerable part of a home because embers lodge there. An Interlock® roof is Class A Fire Rated Available, as a complete assembly.

Which building code applies to a re-roof in Idaho?

Idaho's adopted residential code is the 2018 International Residential Code with Idaho amendments (the Idaho Residential Code, 2020 Edition), according to DOPL. Your city enforces it through the building permit.

Sources

  1. East Idaho News, June 27, 2026: "Lightning, hail, heavy rain hit Boise area, causing flooding, emergency declarations"
  2. NOAA National Centers for Environmental Information: Storm Events Database
  3. University of Idaho, Department of Civil Engineering: Ground Snow Loads for Idaho, 2015 Edition
  4. Ready, Set, Go!: Idaho Personal Wildland Fire Action Guide (Idaho Department of Lands, PDF)
  5. Boise City Code 5-12-53: IFC amendment adding Chapter 41, Wildland-Urban Interface (WUI) Code
  6. Idaho Division of Occupational and Professional Licenses: Idaho Adopted Codes (PDF)
  7. National Weather Service Boise: Boise area climate
  8. ICC-ES Evaluation Report ESR-1790, Interlock Roofing, reissued September 2025 (PDF)
  9. Guardian Lifetime Limited Material Warranty (full document, PDF)

Product specifications are the manufacturer's (Interlock Roofing). Reviewed by Scott Plumptree, October 8, 2026.

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