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Snow Load Report

1. Roof and Building Data

Ground Snow Load (Pg): 40.0 psf
Roof Pitch: 4 /12
Risk Category: II  
Eave-to-Ridge (W): 13 ft.
Terrain Category: C  
Exposure: Partially Exposed  
Thermal Factor (Ct): 1.10  
Roof Surface: Metal  
Roof System: Rafter  
Spacing: 24 in. o/c
Overhang: 12 in.

2. Design Loads

Top Chord Dead Load: 7 psf 
Bottom Chord Dead Load: 10 psf 
SF (Slope Factor) = 1/Cosine(Φ) = 1.05 (Dead loads specified on a projected horizontal basis take into account the effect of the pitch via a slope factor.)
Adj. TCDL (TCDL x SF): 7.4 psf 

3. Design Assumptions

Code Standard: ASCE 7-10
Number of Plies: 1 PLY
Bottom Chord Pitch: 0 /12

4. Snow Load Calculations

Calculate flat roof snow load pf using the following equation:

pf = 0.7CeCtIspg

where:

pf = Flat Roof Snow Load in psf
Ce = 1.00 = Exposure Factor, as determined by ASCE 7-10 Table 7-2 (Terrain Cat. C, Exp. Partially Exposed)
Ct = 1.10 = Thermal Factor, as determined by ASCE 7-10 Table 7-3
Is = 1.00 = Importance Factor, as determined by ASCE 7-10 Table 1.5-2 (Risk Cat. II)
pg = 40.0 psf = Ground Snow Load in psf

pf = 0.7CeCtIspg = 0.7(1.00)(1.10)(1.00)(40.0) = 30.8 psf
Snow Loads 2024A481
N. Wilkerson MEDEEK ENGINEERING INC.
3050 State Route 109 Copalis Beach, WA 98535
ph. (425) 420-5715    www.medeek.com 		-
6/4/2024 1
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A minimum roof snow load, pm shall apply to monoslope, hip and gable roofs with slopes less than 15 degrees using the following equations:

Where pg is 20 psf or less: pm=Ispg
Where pg exceeds 20 psf: pm=Is(20)

Roof slope is greater than 15 degrees, the minimum roof snow load, pm, does not apply.
For locations where pg is 20 psf or less, but not zero, all roofs with slopes (in degrees) less than W/50 with W in feet shall included a 5 psf rain-on-snow surcharge load. This additional load applies only to the sloped roof (balanced) load case and need not be used in combination with drift, sliding, unbalanced, minimum, or partial loads.

Roof slope in degrees (18.43°) is greater than W/50 = 0.3, the 5.0 psf rain-on-snow surcharge load does not apply.
Calculate sloped roof snow load ps using the following equation:

ps = Cspf

where:

ps = Sloped Roof Snow Load in psf
Cs = 1-[(18.43-10)/60] = 0.86 = Roof Slope Factor, as determined by ASCE 7-10 Sec. 7.4.1-7.4.4 and Figure 7-2
pf = Flat Roof Snow Load in psf

Roof surface (Metal) is considered a "slippery" roof. For a Ct = 1.10 the roof slope factor Cs is given by the dashed line of ASCE 7-10 Figure 7-2b.

ps = Cspf = (0.86)(30.8) = 26.5 psf
Calculate unbalanced snow load for hip and gable roofs as shown in ASCE 7-10 Figure 7-5.
Unbalanced snow loads are required for roof pitches between 1/2 on 12 to 7 on 12.
Using the following equations:

γ = 0.13pg + 14 (snow density)
(drift height) [if lu < 20 ft., use lu = 20 ft.]
(width of drift surcharge)
(drift surcharge snow load)

where:

γ = Snow density in pcf, not to exceed 30 pcf.
hd = Drift height in feet, as determined by eqn. or ASCE 7-10 Fig. 7-9.
lu = W = Ridge to eave distance in feet, windward side of roof.
S = 12/Roof Pitch
ld = Width of drift surcharge in feet.
pd = Drift Surcharge Snow Load in psf
Snow Loads 2024A481
N. Wilkerson MEDEEK ENGINEERING INC.
3050 State Route 109 Copalis Beach, WA 98535
ph. (425) 420-5715    www.medeek.com 		-
6/4/2024 2
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For a roof rafter system with W ≤ 20 ft., the simplified unbalanced snow load
is given by the third diagram of ASCE Figure 7-5.

pwindward = 0.0 psf
pleeward = Ispg = (1.00)(40.0) = 40.0 psf
On warm roofs apply a distributed 2pf snow load on all overhanging portions as per ASCE 7-10 section 7.4.5.
No other loads except dead loads shall be present on the roof when this uniformly distributed load is applied.

2pf = (2)(30.8) = 61.6 psf

13 ft.
7.4 psf
7.4 psf
26.5 psf
26.5 psf
10 psf
12 in.
 R1 = 1120.1 lbs
R2 = 1120.1 lbs 
 12  
|4
Out-to-out Span = 24.0 ft.
R1 = D + S = 431.8 lbs + 688.3 lbs
R2 = D + S = 431.8 lbs + 688.3 lbs
Snow Loads 2024A481
N. Wilkerson MEDEEK ENGINEERING INC.
3050 State Route 109 Copalis Beach, WA 98535
ph. (425) 420-5715    www.medeek.com 		-
6/4/2024 3
Subject
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Location
Job No.
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Rev.
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13 ft.
7.4 psf
7.4 psf
0.0 psf
40.0 psf
10 psf
12 in.
 R1 = 670.2 lbs
R2 = 1233.5 lbs 
 12  
|4
R1 = D + S = 431.8 lbs + 238.3 lbs
R2 = D + S = 431.8 lbs + 801.7 lbs
 
13 ft.
7.4 psf
7.4 psf
61.6 psf
61.6 psf
10 psf
12 in.
 R1 = 555.0 lbs
R2 = 555.0 lbs 
 12  
|4
R1 = D + S = 431.8 lbs + 123.2 lbs
R2 = D + S = 431.8 lbs + 123.2 lbs

*Disclaimer: The calculations produced herein are for initial design and estimating purposes only. The calculations and drawings presented do not constitute a fully engineered design. All of the load cases required to fully design an actual structure are not provided by this calculator. For the design of an actual structure, a registered and licensed professional should be consulted as per IRC 2012 Sec. R802.10.2 and designed according to the minimum requirements of ASCE 7-10. The snow load calculations provided by this online tool are for educational and illustrative purposes only. Medeek Design assumes no liability or loss for any designs presented and does not guarantee fitness for use.
Snow Loads 2024A481
N. Wilkerson MEDEEK ENGINEERING INC.
3050 State Route 109 Copalis Beach, WA 98535
ph. (425) 420-5715    www.medeek.com 		-
6/4/2024 4