Gambrel (Barn) Roof Snow Load Calculator
A gambrel (barn) roof has a steep lower slope and a shallow upper slope. The shallow upper slope carries the most snow, so use it for the balanced load, and check the unbalanced case where snow drifts over the ridge.
The worksheet
ASCE 7-22At 20° the §7.3.4 minimum does not apply, so the balanced load of 25.2 psf governs.
≈ 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 20.09 psf over 8.22 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.
Sheds & barns rated for snow
Your design roof snow load is 25.2 psf. Metal and resin shed kits list a roof snow-load rating. Confirm it clears the design load above, especially for an unheated shed (Ct = 1.2).
Arrow, Suncast and Lifetime shed kits. The heavier-gauge and peak-roof models carry more snow.
Shop shed kitsTruss and rafter reinforcement kits that raise a kit shed's snow rating in a heavy-snow region.
Shop reinforcement kitsSome 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 gambrel / barn roof roofs
- Enter the upper (shallow) slope, because it is the one that holds snow. The steep lower slope sheds and is rarely the governing balanced case.
- Barns are usually unheated (Ct = 1.2), and gambrel roofs are classic unbalanced-snow shapes.
Notes & questions
01How is snow load different on a gambrel roof?+
The shallow upper slope governs the balanced load because it sheds the least snow. Use that slope in the calculator, and have the unbalanced load case checked since snow drifts across the shallow top.
02What slope do I enter for a barn roof?+
Enter the upper, shallower slope of the gambrel, since that's where snow accumulates. The steep lower slope sheds snow and rarely controls the balanced design.