Pitched Roof Snow Load Calculator
Pitched roofs shed snow, so the slope factor Cs reduces the load as the pitch steepens. Steep, slippery roofs shed the most, but gable roofs must also be checked for the unbalanced (drifted-leeward) load case.
The worksheet
ASCE 7-22At 27° the §7.3.4 minimum does not apply, so the balanced load of 21 psf governs.
≈ 31,500 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 23.77 psf over 6.95 ft · hd 1.86 ft · γ 17.9 pcf
Flat-roof load Pf = 0.7 × Ce(1) × Ct(1) × Is(1) × Pg(30) = 21 psf. Sloped-roof balanced load Ps = Cs(1) × Pf = 21 psf.
| Ground snow load, Pg | 30 psf | site input |
| Exposure factor, Ce | 1 | Table 7.3-1 |
| Thermal factor, Ct | 1 | 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 | 14 in | design ÷ density |
- 01Estimated snow density ≈ 17.9 pcf, so 21 psf is roughly 14 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.
Reduce the load on an existing roof
Your design roof snow load is 21 psf. If the design load is close to your roof's capacity, the cheapest fix is to keep snow off it. These are the tools that do that.
A long-handled rake pulls snow off from the ground, cutting the load before it builds up. The first thing to buy in a heavy winter.
Shop roof rakesSelf-regulating heat cable along eaves and valleys stops the ice dams that trap meltwater and add weight.
Shop heat cableSome 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 pitched / gable roof roofs
- A common 6:12 pitch is about 26.6°. On a warm, non-slippery roof the slope factor only starts reducing the load above 30°.
- Slippery surfaces (metal, membrane) shed sooner: their slope reduction starts at just 5° on a warm roof.
Notes & questions
01Does a steeper roof have less snow load?+
Yes. Above the breakpoint slope the ASCE 7 slope factor Cs reduces the balanced load linearly to zero at 70°. But a steeper gable roof also drifts more snow to the leeward side, so the unbalanced case can govern.
02What slope sheds snow best?+
Steeper is better, and a slippery surface helps. A metal roof above ~30–40° sheds most snow, but always design for the snow that can still accumulate, especially in the unbalanced and sliding cases.