Page
8
Unirac Code-Compliant Installation Manual
SunFrame
R
1411 Broadway Boulevard NE
Albuquerque NM 87102-1545 USA
15
1.00
1.21
1.47
20
1.00
1.29
1.55
25
1.00
1.35
1.61
30
1.00
1.40
1.66
35
1.05
1.45
1.70
40
1.09
1.49
1.74
45
1.12
1.53
1.78
50
1.16
1.56
1.81
55
1.19
1.59
1.84
60
1.22
1.62
1.87
B
C
D
Table 4. Adjustment Factor (
λ
)
for Roof Height &
Exposure Category
Source: ASCE/SEI 7-05, Minimum Design Loads for Buildings and Other
Structures, Chapter 6, Figure 6-3, p. 44.
Exposure
Mean roof
height (ft)
Step 7: Determine
adjustment factor for height and
exposure category
,
λ:
Using the
Exposure Category
(
Step 6
) and the
roof height, h
(ft)
, look up the
adjustment factor for height and exposure
in
Table 4
.
Step 8: Determine the
Importance Factor, I:
Determine if the installation is in a hurricane prone region .
Look up the
Importance Factor, I
,
Table 6, page 9
, using the
occupancy category description and the hurricane prone
region status .
Step 9: Calculate the
Design Wind Load,
p
net
(psf):
Multiply the
Net Design Wind Pressure
,
p
net30
(psf)(
Step 4
) by
the
adjustment factor for height and exposure
,
λ
(
Step 7
),the
Topographic Factor
,
K
zt
(Step 5), and the
Importance Factor, I
(
Step 8
) using the following equation:
p
net
(psf) =
λ
K
zt
I
p
net30
p
net
(psf)
= Design Wind Load (10 psf minimum)
λ
= adjustment factor for height and exposure category
(
Step 7
)
K
zt
= Topographic Factor at mean roof height, h (ft)
(
Step 5
)
I
= Importance Factor
(
Step 8
)
p
net30
(psf)
= net design wind pressure for Exposure B, at height
= 30, I = 1
(
Step 4
)
Use
Table 5
below to calculate Design Wind Load .
The Design Wind Load will be used in
Part II
to select the
appropriate SunFrame Series rail, rail span and foot spacing .
Variable Description
Symbol
Value
Unit
Step
Reference
Building Height
h
ft
Building, Least Horizontal Dimension
ft
Roof Pitch
degrees
Exposure Category
6
Basic Wind Speed
V
mph
1
Figure 1
Effective Roof Area
sf
2
Roof Zone Setback Length
a
ft
3
Table 1
Roof Zone Location
3
Figure 2
Net Design Wind Pressure
p
net30
psf
4
Table 2, 3
Topographic Factor
K
zt
x
5
Adjustment factor for height and exposure category
λ
x
7
Table 4
Importance Factor
I
x
8
Table 5
Total Design Wind Load
p
net
psf
9
Table 5. Worksheet for Components and Cladding Wind Load Calculation: IBC 2009, ASCE 7-05
