Calculators / Snow Loads

Free Snow Load Calculator

Calculate balanced flat-roof, sloped-roof, and applicable minimum snow loads, plus snow drifts at roof projections and parapets. Select the ASCE 7 edition and project conditions to generate an edition-specific calculation with a free live PDF report.

ASCE Hazard Tool

Code Edition

Structural design code

Ground Snow,

p_g

ASCE 7-22: Figure 7.2-1

Risk Category

ASCE 7-22: Table 1.5-1

Winter Wind Parameter,

W_2

ASCE 7-22: Figure 7.6-1

Snow Region

Region Description

Roof R-value (h·ft²·°F/Btu)

ASCE 7-22: §7.3.2

Balanced Flat Roof Snow Load

p_f = 0.7 C_e C_t p_g

(ASCE 7-22: Eq. 7.3-1)

Exposure Factor,

C_e

ASCE 7-22: Table 7.3-1

Thermal Condition

ASCE 7-22: §7.3.2

Thermal Factor,

C_t

ASCE 7-22: Table 7.3-3

Ground Snow Load Factor,

p_g

ASCE 7-22: Figure 7.2-1

Balanced Flat Roof Load,

p_f

Balanced Sloped Roof Snow Load

p_s = C_s p_f

(ASCE 7-22: Eq. 7.4-1)

Roof Obstructions/Friction

User Defined

Roof Slope,

\\theta

User Defined

Thermal Factor,

C_t

ASCE 7-22: Table 7.3-3

Slope Factor,

C_s

ASCE 7-22: §7.4.1

Balanced Sloped Roof Load,

p_s

Minimum Snow Load

p_m = \min(p_g,\ p_{m,\max})

(ASCE 7-22: §7.3.3)

pm,max from Table 7.3-4 — RC I: 25, II: 30, III: 35, IV: 40 psf

Minimum snow loads apply to monoslope, hip, and gable roofs with slopes below 15°. The roof slope of 18.0° exceeds this limit, so p_m does not apply.

Minimum Roof Snow Load,

p_m

ASCE 7-22: §7.3.3

Governing Balanced Snow Load

Balanced sloped roof load (pm not applicable)

Drift Loads for Roof Projections and Parapets

\gamma = 0.13\,p_g + 14 \le 30\ \text{pcf}

[Snow density]

h_b = p_s / \gamma

[Height of balanced snow load]

h_c = h_{pt} - h_b

[Clear height from balanced snow to top of parapet]

h_d = 0.75\times 1.5\sqrt{\dfrac{p_g^{0.74} l_u^{0.70} W_2^{1.7}}{\gamma}} \le h_c

[Max drift height]

w = 4h_d

[Snow drift width]

p_d = h_d\gamma

[Max drift load]

(ASCE 7-22: Eq. 7.6-1 / §7.8)

Location	Upwind Fetch, $l_u$ (ft)	Parapet Height, $h_{pt}$ (ft)	Action

Location	Balanced Height, $h_b$	Clear Height, $h_c$	Drift Height, $h_d$	Drift Load, $p_d$	Drift Width, $w$	Total, $p_{total}$
Parapet 1	1.16 ft	2.34 ft	2.34 ft	41.9 psf	18.7 ft	62.6 psf

Also in Prose Desktop Prose Desktop only

Unbalanced snow on hip and gable roofsEvaluates windward and leeward roof loading patterns.
Ice dams along eavesCalculates eave surcharge where meltwater can refreeze.
Sliding snow loadChecks snow sliding from an upper roof onto a lower roof.
Drift loads at roof stepsCalculates windward and leeward drift at elevation changes.
Rain-on-snow surchargeAdds the applicable rain surcharge to roof snow loading.

This free web calculator evaluates one roof region at a time. Unbalanced snow, roof-step drifts, sliding snow, ice dams, and rain-on-snow are available in Prose Desktop.

See Prose Desktop

About the Free Snow Load Calculator

What the calculator does

The Free Snow Load Calculator converts site ground snow load and roof conditions into code-referenced roof design loads. It provides a live calculation report that can be downloaded as a PDF for project documentation and independent engineering review.

Supported snow-load calculations

Balanced flat roof snow load
Balanced sloped roof snow load
Minimum roof snow load by risk category
Snow drift at roof projections and parapets
Exposure, thermal, slope, density, drift-height, and drift-width factors

Supported ASCE editions

Calculations support ASCE 7-10, ASCE 7-16, and ASCE 7-22. Equations, minimum-load rules, risk-category treatment, snow importance factors, and winter wind parameters change with the selected edition.

Use this roof snow load calculator with a ground snow load from the ASCE Hazard Tool and confirm the result against the governing building code and local jurisdiction.