Tools
Roof Snow Load Calculator
A free tool that estimates flat-roof snow load from the ground snow load using the ASCE 7-22 factors.
Roof snow load calculator
Your roof carries less than the ground because wind and a heated interior shed snow.
Educational estimate for a flat or low-slope roof. Drifting, sliding, sloped roofs, and rain-on-snow need a licensed engineer. ASCE 7-22 also sets a minimum roof load, so very low results are floored by code.
In plain terms
Think of the ground snow load as the snow piled in your yard. Your roof sees less of it, because wind blows some off and a heated house melts it from below. So you start at about 70 percent of the ground number, then nudge it up or down for your roof.
Rule of thumb: for a normal heated house on an open lot, the roof load is roughly three quarters of the ground number. At a ground load of 30 psf that is about 20 psf.
What each part means
| Symbol | Plain meaning | Which way it pushes | Typical |
|---|---|---|---|
| 0.7 | Roofs shed about 30 percent | fixed | 0.7 |
| Ce | How exposed the site is | windy and open lowers it, sheltered raises it | 0.9 to 1.2 |
| Ct | How warm the building is | unheated raises it | 1.0 to 1.2 |
| Is | How critical the building is | hospitals and essential buildings raise it | 0.8 to 1.2 |
| pg | Snow on the ground (map or AHJ) | the starting number | local |
A worked example
Worked example. A Denver home with a ground snow load of 30 psf, typical exposure, heated, normal risk: 0.7 x 1.0 x 1.0 x 1.0 x 30 = about 21 psf on the flat roof.
Related questions
Questions this tool answers
Short answers below, with a link to the full write-up on each.
How do I prevent snow and ice damage to my garage door?
Replace cracked bottom seals before winter, lubricate hinges and springs with silicone or white lithium spray in fall, and clear snow from the door path before it refreezes.
Read full answerReference & standards
The codes and standards behind it
The engineering sources this tool is built on.
- ASCE 7-22 Chapter 7 - Snow Loads: The Engineering Standard Behind Colorado Garage Door Structural RequirementsASCE 7-22 Chapter 7 defines how to calculate roof snow loads from ground snow load values.
- Larimer County Structural Design Criteria for Garage Door SpecificationsLarimer County publishes structural design information used for all building permits in unincorporated areas and as a reference by Fort Collins, Loveland, and other municipalities.
- City of Aurora Climatic Design Criteria for Garage Door SpecificationsAurora Municipal Code Section 22-186 sets climatic design criteria for all building permits in the City of Aurora: ground snow load 40 psf, ultimate design wind speed 115 mph, wind exposure C.
- Jefferson County Climatic and Geographic Design Criteria for Garage Door Structural SpecsJefferson County does not publish a single snow load value for the whole county.
- 2025 Denver Building Code - Adopted Codes and Key Provisions for Garage DoorsDenver adopted new building codes effective June 13, 2025, based on the 2024 IBC and 2024 IRC with Denver-specific amendments.
- Denver DRC Table R301.2(1) - Climatic and Geographic Design Criteria for Garage Door SpecsDenver's 2025 Residential Code sets key design values for garage door selection and permitting: ground snow load 43 psf (raised from 35 psf in 2025), Vult wind speed 115 mph, Exposure C, frost depth 36 inches, and Seismic Design Category B.
- SEAC 2016 Colorado Design Snow Loads - Ground Snow Load Map for Front Range JurisdictionsThe SEAC 2016 Colorado Design Snow Loads document is the reference map used by Front Range jurisdictions to determine ground snow load for structural design.
- DASMA TDS 196 - U-Factor Ratings and the DASMA Thermal Performance Verification ProgramDASMA TDS 196 explains the DASMA Thermal Performance Verification Program, which validates manufacturer-published U-factor values for garage doors using independent testing under ANSI/DASMA 105.
Need a door that meets code?
We install to Colorado and Denver-metro requirements every day. Get a free, no-pressure estimate.