ROOF SNOW LOAD

EVERY ASCE 7-22 ROOF SNOW LOAD CASE IN ONE CALCULATION

The Roof Snow Load Calculator determines balanced, minimum, drift, sliding, and unbalanced roof snow loads to ASCE 7-22 Chapter 7. The tool can be deployed for a light-gauge steel or any other building structure.

Complex resilient channel cold-formed steel section fabricated using Scottsdale K35C roll forming machine.

ScotCalc — Roof Snow Load

Scottsdale Construction Systems

ScotCalc

Engineering Tools

Roof Snow Load v1.15

Balanced, minimum and drift snow loads under ASCE 7-22 Chapter 7.

1Site and ground snow load

Risk Category (IBC Table 1604.5)

Ground snow load, p_g

psf

Use the value for the Risk Category selected above. ASCE 7-22 ground snow loads are strength-level values that differ by Risk Category. You can look up the value for a site address on the free ASCE Hazard Tool.

2Exposure factor, C_e

Surface roughness

Roof exposure

A roof is fully exposed when nothing shelters it from the wind: no terrain, higher structures or trees nearby. It is sheltered when it sits tight among conifers or other obstructions that qualify under ASCE 7-22 Table 7.3-1. Most roofs are partially exposed.

3Thermal factor, C_t

Thermal condition (ASCE 7-22 Table 7.3-2)

Roof thermal resistance, R_roof

h·ft²·°F/Btu

C_t is interpolated from roof R-value and ground snow load. A roof with an R-value above 50 (8.80 m²·K/W) uses C_t = 1.2.

4Roof geometry and surface

Roof type

Slope entered as

Roof slope

: 12

Eave-to-ridge distance, W

W is the horizontal distance from eave to ridge. For a monoslope roof, enter the full horizontal width from the low eave to the high eave. W is used for the rain-on-snow check and, on gable and hip roofs, as the fetch for the unbalanced load.

Roof members are simply supported and prismatic, spanning from eave to ridge (used for the unbalanced load when W is 20 ft or less)

Roof surface

A slippery surface qualifies only if snow is free to slide off the eave. Snow guards, parapets and other obstructions remove the slippery-surface reduction. Shingles and membranes with embedded granules or aggregate are not slippery.

Governing uniform load

—

Balanced, p_s

—

Minimum, p_m

—

Factors

Item	Basis	Value

Calculation

Snow drifts and sliding snow (ASCE 7-22 Sections 7.7, 7.8 and 7.9)

Winter wind parameter, W₂

Look up W₂ on the free ASCE Hazard Tool, where it is reported with the ground snow load. It is the fraction of time from October through April that the wind exceeds 10 mph.

Drifts are calculated on the roof defined above, which receives the drift. Its balanced load p_s sets the depth of balanced snow, h_b. Add each roof step, parapet or rooftop unit that can collect drifting snow. Each location is checked for both leeward and windward drifts where the code requires it.

Prints a step-by-step calculation report of everything above, with the essential figures. Choose "Save as PDF" in the print dialog to keep a copy.

ScotCalc · Roof Snow Load

All loads per ASCE 7-22 Chapter 7, the standard referenced by the 2024 IBC. Preliminary estimate. Intersecting drifts (Section 7.7.3) are not yet included. Final design loads must be confirmed by the engineer of record and the authority having jurisdiction.

ROOF SNOW LOAD

EVERY ASCE 7-22 ROOF SNOW LOAD CASE IN ONE CALCULATION

Roof Snow Load v1.15

Factors

Calculation

Snow drifts and sliding snow (ASCE 7-22 Sections 7.7, 7.8 and 7.9)

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