Snow Drift Loading
Adjacent to Roof Obstructions (NBC2020)
v1.0.0
File:
Project:
Designer:
Date:

Climatic Data

Location
Province:
Ground snow load
Ss:
Rain Load
Sr:
Density
Snow density, γ:
kN/m3 *If left blank, γ will calc as per cl. 4.1.6.13

Factors

Importance factor
Is:
Factors
Cb:
*Optional
Cw:
snow drift distribution

Roof Projection

Length, l0:
m
Height, h:
m

Roof geometry

Pitch:
/12
Slippery:
Longer dimension, L:
m
Shorter dimension, w:
m

*L and w only changes results if no Cb provided

Specified Snow Load

[4.1.6.2]
S = Is[Ss(CbCwCsCa)+Sr]

Factors

User input values:
Ss = 1 kPa
Sr = 1 kPa
Importance Factors
ULS: Is = 1.0
SLS: Is = 0.9
Roof slope = 0 degrees
Slope Factor
For non-slippery roof:
Slope <= 30 degrees.
Cs = 1
Cb = 0.8
Density = γ = 2.6 kN/m3
[4.1.6.7]

Drift Factors & Distribution


Ca(0) = lesser of:
a) Ca0=0.67*γ*h/(Cb*Ss) =6.533
b) Ca0=(γ*l0/(7.5*Cb*Ss))+1 =2.733

Ca(0) = 2.73


xd = lesser of:
a) xd = 3.35*h =10.05 m
b) xd = (2/3)*l0 =2.67 m

xd = 2.67m


h' = h - CbCwSs/γ = 2.692m

Min dist where (Cw = 1.0) = 10*h' = 26.923 m

Obstruction effect limit = 3 m

Snow Load Summary

( b = 4 m ) >= ( 3 m )

x = 0

Cw = 1
Ca(0) = 2.7333

SULS = 1.0[1(0.8*1*1*2.733)+1] = 3.187 kPa

SSLS = 0.9[1(0.8*1*1*2.733)+1] = 2.868 kPa

0 < x ≤ ( xd = 2.667m )

Cw = 1
Ca(x) decreases linearly over 0 < x ≤ xd
Ca(x) = 2.7333 - 0.65 * x   (with x in meters)

x = xd = 2.667m

Cw = 1
Ca(xd) = 1

SULS = 1.0[1(0.8*1*1*1)+1] = 1.8 kPa

SULS = 0.9[1(0.8*1*1*1)+1] = 1.62 kPa

x > ( xd = 2.667m )

Cw = 1.0
Ca(x) = 1

SULS = 1.0[1(0.8*1.0*1*1)+1] = 1.8 kPa

SSLS = 0.9[1(0.8*1.0*1*1)+1] = 1.62 kPa

This information must be read or used in conjunction with Part 4 of the NBCC 2020. In the event of discrepancies, Part 4 of the NBCC 2020 shall govern.