What is the roof snow load for a Colorado mountain home?

What does snow load psf mean?

• Pounds per square foot. It is the weight of snow and ice a roof is designed to carry over each square foot.
• Dry snow is light. One foot of light dry snow weighs 3 psf, per the DOE Building America Solution Center.
• Wet snow is heavy. One foot of heavy wet snow weighs 21 psf, seven times the dry number.
• Ice is heavier. Ice adds 5 psf per inch.
• What 70 psf holds. At 21 psf per foot, a 70 psf ground load equals 3.3 feet of heavy wet snow.

What is the snow load in Jefferson County, Colorado?

• Below 6,500 feet: 43 psf ground, 30 psf roof. From the county's 2024 building code supplement.
• 7,000 feet: 54 psf ground, 38 psf roof. Evergreen's USGS map point sits at 7,056 feet.
• 7,625 feet: 70 psf ground, 49 psf roof. That is the limit for the IRC's prescriptive design.
• 8,000 feet: 82 psf. 9,000 feet: 114 psf. Conifer's map point sits at 8,262 feet.
• 10,000 feet: 152 psf. 10,500 feet: 172 psf. Above 70 psf, the county requires a registered design professional.

Ask the building department that covers the lot for the design snow load before you buy land or plan an addition.

What do other Colorado mountain counties require?

• Larimer County. Ground snow load runs 55 psf at 5,000 feet, 95 psf at 7,000 feet, 110 psf at 8,000 feet and 160 psf at 9,000 feet. Roof snow load never drops below 35 psf.
• Larimer's method. The county multiplies the SEAC 2016 Colorado Design Snow Loads values by 1.6 and runs the 2024 IRC and IBC.
• Clear Creek County. The county sets snow load by property through its ClearMap tool and allows no snow load reductions.
• Park County. Snow and wind loads come from the ASCE 7-22 Hazard Tool for plans submitted on or after January 1, 2024.

What other climate design rules apply in the mountains?

• Frost depth. 36 inches in Jefferson County, 42 inches for foundations in Clear Creek County and 30 inches in Larimer County.
• Winter design temperature. 1°F in Jefferson County and -10°F in Clear Creek County.
• Ice barrier. Jefferson County and Clear Creek County both require ice barrier underlayment.
• Wind. Jefferson County lists a 129 mph design wind speed.

What roof pitch lets snow slide off?

• Under 30 degrees holds snow. Roofs under 30 degrees of slope do not see significant snow sliding, per the DOE Building America Solution Center.
• Steeper roofs shed. Snow that slides lands at the eave, on decks, walkways and window wells.
• Snow guards trade one load for another. They reduce roof slides and raise the snow load where they hold snow.

On a showing, look at where each roof plane drops its snow: doors, decks, driveways and meters.