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SunFrame
Unirac Code-Compliant Installation Manual
R
1411 Broadway Boulevard NE
Albuquerque NM 87102-1545 USA
The procedure to determine Design Wind Load is specified
by the American Society of Civil Engineers and referenced in
the International Building Code 2009 . For purposes of this
document, the values, equations and procedures used in this
document reference ASCE 7-05, Minimum Design Loads for
Buildings and Other Structures .
Please refer to ASCE 7-05 if
you have any questions about the definitions or procedures
presented in this manual.
Unirac uses Method 1, the
Simplified Method, for calculating the Design Wind Load for
pressures on components and cladding in this document .
The method described in this document is valid for flush, no
tilt, SunFrame Series applications on either roofs or walls .
Flush is defined as panels parallel to the surface (or with no
more than 3” difference between ends of assembly) with no
more than 10” space between the roof surface, and the bottom
of the PV panels .
This method is not approved for open structure calculations .
Applications of these procedures is subject to the following
ASCE 7-05 limitations:
1 . The building height must be less than 60 feet, h < 60 . See
note for determining h in the next section . For installations
on structures greater than 60 feet, contact your local Unirac
Distributor .
2 . The building must be enclosed, not an open or partially
enclosed structure, for example a carport .
3 . The building is regular shaped with no unusual geometrical
irregularity in spatial form, for example a geodesic dome .
4 . The building is not in an extreme geographic location such
as a narrow canyon or steep cliff .
5 . The building has a flat or gable roof with a pitch less than 45
degrees or a hip roof with a pitch less than 27 degrees .
6 . If your installation does not conform to these requirements
please contact your local Unirac distributor, a local
professional engineer or Unirac
If your installation is outside the United States or does not
meet all of these limitations, consult a local professional
engineer or your local building authority . Consult ASCE 7-05
for more clarification on the use of Method I . Lower design
wind loads may be obtained by applying Method II from ASCE
7-05 . Consult with a licensed engineer if you want to use
Method II procedures .
The equation for determining the Design Wind Load for
components and cladding is:
p
net
(psf) =
λ
K
zt
I
p
net30
p
net
(psf) = Design Wind Load
λ
= adjustment factor for building height and exposure category
K
zt
= Topographic Factor at mean roof height, h (ft)
I = Importance Factor
p
net30
(psf) = net design wind pressure for Exposure B, at height
= 30 ft, I = 1.0
You will also need to know the following information:
Basic Wind Speed = V (mph), the largest 3 second gust of wind in
the last 50 years.
h (ft) = total roof height for flat roof buildings or mean roof
height for pitched roof buildings
Effective Wind Area (sf) = minimum total continuous area of
modules being installed
Roof Zone = the area of the roof you are installing the pv system
according to Figure 2, page 5.
Roof Zone Setback Length = a (ft)
Roof Pitch (degrees)
Exposure Category
Part I.
Procedure to Determine the Design Wind Load
[1.1.] Using the Simplified Method - ASCE 7-05:
[1.2.] Procedure to Calculate Total Design Wind:
The procedure for determining the Design Wind Load can be
broken into steps that include looking up several values in
different tables .
Step 1: Determine
Basic Wind Speed, V (mph):
Determine the
Basic Wind Speed, V (mph)
by consulting your
local building department or locating your installation on the
maps in
Figure 1, page 4
.
Step 2: Determining
Effective Wind Area:
Determine the smallest area of continuous modules you will
be installing . This is the smallest area tributary (contributing
load) to a support or to a simple-span of rail . That area is the
Effective Wind Area .
