Civil Engineering Reference
In-Depth Information
Figure G4-2
Uniform design roof
snow load and
elevation of a
monoslope roof for
Example 4-1.
the minimum roof snow load becomes (
I
s
) (
p
g
) or 24 lb/ft
2
. The uniform design
roof snow load is 24 lb/ft
2
as shown in
Figure G4-2.
Refer to Example 5-2 for the partial loading of this roof structure.
Example 4-2
Uniform Roof Snow Load,
Monoslope Roof (4 on 12)
Problem
Solve the same problem as Example 4-1, except the monoslope roof is 4 on
12 and has an unobstructed, slippery roof surface.
Solution
From Example 4-1, the fl at roof snow load is 18.5 lb/ft
2
, with
I
s
=
1.2 and
C
t
1.1. From the equations in the ASCE 7-10 Commentary for a 4-on-12
(18.4° slope), unobstructed, slippery roof with
C
t
=
=
1.1,
C
s
=
1.0
−
(18.4°
−
10°)/60°
=
0.86
Therefore, the sloped roof snow load is
0.86 (18.5 lb/ft
2
)
15.9 lb/ft
2
(round to 16 lb/ft
2
)
p
s
=
C
s
p
f
=
=
For this comparatively steep slope, there is no need to consider a rain-on-
snow surcharge. Also, since the monoslope is steeper than 15°, there is no
