Building Example: Garage with Gable Roof
(Garage Door & Windows)
This example is to help Windloadcalc.com users understand how to enter information for
a Gable Roof building.
The following will give you the understanding of how to properly enter your building
information and get the wind load calculations needed for door(s), window(s), and your
You will also be given the understanding of how to apply zones to your door(s),
window(s), and roof.
First, you must enter your building’s information.
Reference the images below. The first image is “Building Information”. This is a section
on the program that is required.
The second image is a diagram of the garage that we will be finding wind loads for. The
numbers applied to this diagram are the zone locations; these zones locations are standard
for all buildings according to ASCE 7.
“Building Information” requirements are explained one by one.
(By running your cursor over the top of each description you will be given information, stated from ASCE 7, that
helps you with your entries. This information is provided on each program for quick and
easy reference, but can also be found in the ASCE 7 book; in Chapter 6).
1. Wind Velocity: The number entered in this cell is to have the units
in miles per hour (mph). This is the velocity zone
location that your building is located, according to
the ASCE 7 Basic Wind Speed Map. The map is
provided with the purchase of your programs.
2. Building Category: Make your selection from the pull-down list. The
options are provided in the description given on the
program (place cursor over the top of the
description.) If you need more information on
Building Categories, please reference Table 1-1 in
the ASCE 7 book.
3. Importance Factor: The value is automatically calculated for you, based
on your “Building Category” entry. You can view
the values of the Importance Factor from the
“Building Category” description; when placing your
cursor over the top of the description.
4. Exposure: From the pull-down list you have three (3) choices.
Exposures B, C, & D. (Exposure A was eliminated
after ASCE 7-98). Make your selections based on
the information that is provided is the description.
(The description provided is the same description
you will find in ASCE 7).
5. Internal Pressure: Make your selection from the pull-down list
provided. You have three (3) choices. 1) Partially
Enclosed, 2) Enclosed Building, 3) Open Building.
a. Partially Enclosed: This type of building has
walls under the roof, but also has at least one
side that is exposed or open to the outside.
b. Enclosed: This is the most common. This type
of building has no openings exposed to the
outside. The walls enclose the entire building
under the roof.
c. Open Building: This type of structure has no
walls under the roof, and is completely exposed
to the outside. This would basically be a roof
that is only supported by post, pillars or similar
6. Height Above Ground: This is also know as the value “z”. This value is for
elevated buildings, for the simple fact that the value
of “z” is the dimension from the ground to the
bottom of your building. So if your building is at
ground level, this value would be zero (0).
7. Standard Wall Height: This value is the dimension measured from the
ground to the eave height (or where the lower
portion of your roof meets the side-wall) of your
8. Mean Roof Height: This also known as the value “h”. This value is the
dimension measured from grade to the average of
the roof eave height and the highest point on the
roof surface, except that eave height shall be used
for the roof angle if it is less than or equal to 10
Remember: When h > 60 ft., your roof angle must
be less than or equal to 10 degrees; according to the
Flat Roofs: This will be the actual building height
9. Building Width: This value is the width dimension of your building;
10. Building Length: This value is the length dimension of your building;
11. Roof Slope: This is the value of “x” over twelve; or x/12. You
need to enter a value from 0-12 (Zero (0) is flat, and
twelve (12) is 45 degrees).
12. Roof Angle: This value is automatically calculated and entered
for you. It displays the angle of your roof based on
the value of “x” entered for your roof’s slope.
13. Edge Strip: This value is also known as the value of “a”. This
value is automatically calculated based off of the
building information you entered. The Edge Strip
value (“a”), is used to determine the dimensions of
zone five (5) for your wall sections, and zone (3) for
your roof sections.
14. End Zone: This value is the total Edge Strip value along one
side of your wall. This value is also automatically
calculated for you, based off of the building
information you entered in. It is basically the value
of “a” multiplied by two (2).
All the “Building Information” is entered, next is to find the wind loads for the roof,
door(s), and window(s).
Below is a diagram that shows the garage that we are finding wind loads for. As you can
see the numbers below show the zones for the garage.
1. Zones 1, 2, & 3 are always applied to the roof.
a. Zone 3: are the edge or corner sections; always equal to the value of “a”.
b. Zone 2: are the perimeter sections; minus the Zone 3 (edge/corner) areas.
c. Zone 1: are the interior sections. Basically the interior area left over after
subtracting the areas of the Zone 3, and Zone 2.
2. Zones 4 & 5 are always applied to the walls.
a. Zone 5: are the corner sections; always equal to the value of “a”.
b. Zone 4: are the interior sections; or the area remaining after subtracting the
Zone 5 sections.
3. Remember: The Value of “a” is always applied to the roof and wall corners.
4. Remember: Any door or window dimension that falls within the area of “a”
(edge/corner = Zone 5) section must have the Zone 5 applied to it.
5. Remember: Any opening dimension that falls with the area of “a” (edge/corner =
Zone 3) on the roof (such as a sky-light) must have the Zone 3 applied to it.
Finding Roof Wind Loads:
First find the dimension (from center-to-center) of your roof’s truss frames. For this example our truss frames are dimensioned 3 feet from center-to-center (Reference the diagram below). Building Length is 30ft, and the value of “a” (Edge Strip) is 3 feet.
From this we can determine the areas with our Zones 1, 2, & 3.
= (Value of “a”) x (Value of “a”)
= (3 feet) x (3 feet)
= 9 square feet.
Zone 2 (Perimeter: Width Side)
= (Truss Frame: center-to-center) x (Value of “a”)
= (3 feet) x (3 feet)
= 9 square feet.
Zone 2 (Perimeter: Length Side)
= (Value of “a”) x (Dimension between Zone 3)
= (3 feet) x (8.14 feet)
= 24.42 square feet
Note: Program calculates the precise number, but shows the effective area on the program rounded up.
Zone 1 (Interior Section)
= (Truss Frame: center-to-center) x (Dimension between Zone 3)
= (3 feet) x (8.14 feet)
= 24.42 square feet.
It is not necessary to calculate for each individual area for the zones on the roof since they are equally distributed, meaning the following applies:
Ø All of the areas for Zone 3 = 9 sqft.
Ø All of the (Perimeter: Width Side) Zone 2 = 9 sqft.
Ø All of the (Perimeter: Length Side) Zone 2 = 24.42 sqft.
Ø All of the areas for Zone 1 = 24.42 sqft.
Finding Wall Wind Loads for Window & Doors:
For this example we have:
Door A: Garage Door = W x H = (16 feet x 8 feet) = 128 square feet
Window B: Side Window = W x H = (4 feet x 4 feet) = 16 square feet
Window C: Side Window = W x H = (6 feet x 4 feet) = 24 square feet
Note: The “Opening Elevation” is the dimension measured from the ground to the center point of the opening. The following diagrams show how to determine the “Opening Elevation” for the garage door and the windows.
We are now able to enter in all the information into the Windloadcalc.com Program. The following is the computed spreadsheet.