Snow Load Calculator

Calculate flat roof snow load, sloped roof snow load, and drift loads per ASCE 7 using pf = 0.7CeCtIpg.

Inputs

Ground Snow Load (pg)

psi

ASCE 7-22 Fig 7.2-1: southern US 0–0.5 kPa; mid-Atlantic 1–2 kPa; New England 2–4 kPa

Exposure Factor (Ce)

ASCE 7-22 Table 7.3-1: exposed ridge Ce=0.7; open terrain Ce=0.9; partial Ce=1.0; sheltered Ce=1.2

Thermal Factor (Ct)

Importance Factor (I)

Roof Slope

degrees

Tab to move between fields

Results

Flat Roof Snow Load (pf)

1.05 kPa

Sloped Roof Snow Load (ps)

1.05 kPa

Drift Surcharge Load1.57 kPa

Total Design Snow Load2.62 kPa

How to Use This Calculator

Enter the ground snow load (Pg) from ASCE 7 Figure 7.2-1 for your location in psf.
Set the roof slope in degrees and the exposure category (fully exposed, partially exposed, sheltered).
Input the thermal factor Ct (heated, unheated, or cold storage) and the importance factor Is.
Review the Flat Roof Snow Load (Pf) and the Sloped Roof Snow Load (Ps).
Add drift or sliding snow loads for adjacent higher roofs if applicable.

How the result changes with Ground Snow Load (pg)

Ground Snow Load (pg)	Flat Roof Snow Load (pf)	Sloped Roof Snow Load (ps)
1.59	1.11 kPa	1.11 kPa
5.31	3.72 kPa	3.72 kPa
9.79	6.85 kPa	6.85 kPa
14	9.8 kPa	9.8 kPa

What each input means

Ground Snow Load (pg): 50-year mean recurrence interval ground snow load per ASCE 7-22 Figure 7.2-1 or local building code. Typical US values: Southern US 0–0.5 kPa; Mid-Atlantic 1–2 kPa; New England 2–4 kPa; mountainous areas 5–15+ kPa.
Exposure Factor (Ce): Terrain/exposure factor per ASCE 7-22 Table 7.3-1. Ce=0.7: fully exposed (windy, unobstructed ridge/open terrain); Ce=0.9: partially exposed; Ce=1.0: default/partially exposed; Ce=1.1: sheltered; Ce=1.2: dense spruce/fir forest.
Thermal Factor (Ct): Thermal condition factor. 1.0 = heated, 1.1 = unheated enclosed, 1.2 = unheated open, 1.3 = freezer building.
Importance Factor (I): Risk category importance factor. 0.8 = low risk, 1.0 = normal, 1.1 = substantial, 1.2 = essential.
Roof Slope: Slope of the roof surface in degrees from horizontal.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Ground Snow Load (pg) = 1.5, Exposure Factor (Ce) = 1, Thermal Factor (Ct) = 1, Importance Factor (I) = 1 = 5 input(s) provided
Calculate Flat Roof Snow Load
Flat Roof Snow Load
1.05 = 1.05
Calculate Sloped Roof Snow Load
Sloped Roof Snow Load
1.05 = 1.05
Calculate Drift Surcharge Load
Drift Surcharge Load
1.57 = 1.57
Calculate Total Design Snow Load
Total Design Snow Load
2.62 = 2.62

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