Metal Building & Metal Roof Snow Load Calculator
Steel buildings and standing-seam metal roofs are 'unobstructed slippery surfaces' in ASCE 7, so the slope factor Cs reduces the load at a lower slope than shingles. Unheated metal buildings also use a higher thermal factor Ct.
The worksheet
ASCE 7-22The balanced load of 25.2 psf governs (it exceeds the 20 psf minimum).
≈ 37,800 lb total on 1,500 sq ft of roof plan
Large gable roof (W > 20 ft): windward side at 0.3·Ps, leeward side at Ps plus a drift surcharge from the ridge.
surcharge 16.63 psf over 9.93 ft · hd 1.86 ft · γ 17.9 pcf
Flat-roof load Pf = 0.7 × Ce(1) × Ct(1.2) × Is(1) × Pg(30) = 25.2 psf. Sloped-roof balanced load Ps = Cs(1) × Pf = 25.2 psf.
| Ground snow load, Pg | 30 psf | site input |
| Exposure factor, Ce | 1 | Table 7.3-1 |
| Thermal factor, Ct | 1.2 | Table 7.3-2 |
| Importance factor, Is | 1 | Table 1.5-2 |
| Slope factor, Cs | 1 | Fig. 7.4-1 |
| Snow density, γ | 17.9 pcf | Eq. 7.7-1 |
| Settled depth at design load | 17 in | design ÷ density |
- 01Estimated snow density ≈ 17.9 pcf, so 25.2 psf is roughly 17 in of settled snow.
- 02The §7.6.1 unbalanced (leeward-drift) case is computed above for this gable/hip roof; at roof steps, parapets and walls also check drift loads (§7.7) with the drift calculator, plus sliding snow (§7.9) onto anything below.
- 03Ground snow load Pg is set by your local building department / the ASCE 7 Hazard Tool. Always confirm the value for your exact site before you build or submit.
Steel buildings engineered to your snow load
Your design roof snow load is 25.2 psf. Steel building kits are engineered to a specified ground snow load. A supplier can certify the frame for the design load above and stamp drawings for your permit.
Get steel building quotes certified for your design snow loadFree, no obligation. We pass your numbers to suppliers so quotes come back accurate.Some links are affiliate links: if you buy through them we may earn a commission at no extra cost to you. These are starting points, not engineering endorsements. Always confirm a product's rated snow load meets the design load above.
Notes for metal building roofs
- A slippery metal roof on a warm building starts shedding (Cs < 1) at just 5°; an unheated metal building (Ct = 1.2) starts at 15°.
- Watch sliding snow off metal roofs onto lower roofs, walks and equipment; it can dump a large load suddenly.
Notes & questions
01Do metal roofs have lower snow loads?+
The design ground snow load is the same, but a metal roof is a slippery surface, so its slope factor reduces the balanced load at a lower pitch than a shingle roof. It sheds snow more readily.
02What snow load should a steel building be designed for?+
Use your site ground snow load with Ct = 1.2 if the building is unheated, the slippery-surface slope factor, and your importance factor. Enter those above to get the design roof snow load in psf.