Snow Load Calculator 2026: 5 Inputs for Your Metal Roof
Snow is one of the main loads a metal building roof has to carry, and it decides how heavy the frame and purlins need to be. This calculator estimates the flat roof snow load for your building using the method in ASCE 7-16, the standard most US building codes refer to. Enter your ground snow load, exposure and building size to see the load in pounds per square foot and the total weight on the roof.
How the Calculator Works
ASCE 7-16 starts with the ground snow load, then adjusts it for the roof:
Flat roof snow load (pf) = 0.7 x Ce x Ct x Is x pg
| Input | What it means | Typical values |
|---|---|---|
| pg, ground snow load | Design snow on the ground at your site, from your local building department or the ASCE hazard tool | 0 to 100+ psf |
| Ce, exposure factor | How much wind blows snow off the roof | 0.9 fully exposed, 1.0 partly, 1.1 to 1.2 sheltered |
| Ct, thermal factor | How warm the building is | 1.0 heated, 1.1 kept just above freezing, 1.2 unheated |
| Is, importance factor | Risk category of the building | 0.8 low risk such as farm buildings, 1.0 normal, 1.1 to 1.2 high occupancy or essential |
| Width and length | Building footprint | Used for total roof load |
For low slope roofs, ASCE 7 also sets a minimum. When pg is 20 psf or less, the minimum is Is x pg. Above 20 psf, it is 20 x Is. The calculator uses whichever is larger.
Worked Example
A 40x60 unheated shop, partly exposed, normal risk, with a ground snow load of 30 psf:
- pf = 0.7 x 1.0 x 1.2 x 1.0 x 30 = 25.2 psf
- Minimum for low slope = 20 x 1.0 = 20 psf, so 25.2 psf governs
- Roof area = 40 x 60 = 2,400 sq ft
- Total snow on the roof = 25.2 x 2,400 = 60,480 lb
That is about 30 tons of snow, which shows why load ratings matter.
Where to Find Your Ground Snow Load
- Your local building department is the final word. Many counties publish a design snow load.
- The ASCE Hazard Tool gives ground snow loads by address based on ASCE 7 maps.
- State amendments in snowy states often set higher values than the national maps, especially in mountains.
What This Calculator Does Not Cover
This is a planning tool, not an engineered design. It does not include:
- Sloped roof factor (Cs), which reduces load on steep, slippery roofs.
- Drifts next to taller buildings, parapets or lean tos, which can be much heavier than the flat load.
- Unbalanced loads on gable roofs when wind moves snow to one side.
- Rain on snow surcharges in some areas.
Your building supplier's engineer will check all of these. Use the result to tell suppliers the load you need and to compare quotes on the same rating.
What It Means for Your Building
Higher snow loads mean heavier frames, closer purlin spacing and sometimes thicker panels, all of which add cost. Tubular carports in snowy areas often need 12 gauge frames and vertical roofs so snow slides off. See our gauge guide and metal roof guide. To price a building rated for your load, use the metal building cost calculator.
Snow Load Tips for Metal Buildings
Order the building rated for the load your county requires, not the lowest option on a quote. Keep the roof clear of obstacles that trap drifts, and avoid adding a lean to or a taller addition without having the engineer check drift loads. After a heavy storm, watch for sagging purlins, popping sounds or doors that suddenly stick, which can be signs of overload. Remove snow from the ground with a roof rake rather than climbing on a loaded roof, and never pile snow from one roof onto another. If in doubt, call your supplier or a local engineer for advice.
FAQ
How do you calculate snow load on a roof?
Under ASCE 7-16, flat roof snow load equals 0.7 times the exposure factor, thermal factor, importance factor and ground snow load.
What is a good snow load rating for a metal building?
It depends on your site. Use the ground snow load from your local building department, then size the roof to the calculated load.
Does roof pitch change snow load?
Yes. Steep, slippery roofs shed snow and can use a lower sloped roof load. This calculator shows the flat roof value, which is conservative.
Sources
- ASCE/SEI 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, Chapter 7, Snow Loads.
- ASCE Hazard Tool, ground snow load lookup, checked October 2026.
Ready to price your building? Get free metal building quotes from suppliers who serve your area, or use the form on this page and our team will be in touch.