When planning a metal building, it's important to know how to determine the final height of the inside from floor to ceiling. To determine the height, you must know:
- The Eave Height
- The Roof Pitch
- The depth of the roof purlins
- the type of slope
- the width of the building.
To determine the ceiling height of a gabled building:
First, take the total width and divide by 2
Total width = 72' 0" / 2 = 36' 0"
Next, look at the roof pitch. The roof pitch is a measure of the slope. It is always measured in twelfths.
If you have a 1/12 pitch, you have 1 foot of rise vertically for every 12 foot of run horizontally
If you have a 2/12 pitch, you have 2 foot of rise vertically for every 12 foot of run horizontally
If you have a 5/12 pitch, you have 5 foot of rise vertically for every 12 foot of run horizontally
In the example above we have 36 foot of horizontal and a 1/12 pitch (in speaking, we say this is a "one on twelve pitch")
So take the horizontal run of 36 feet and divide by 12 (36 divided by 12 = 3)
Next multiply the Rise by this number. So 3 x 1 foot = 3 feet.
This gives you the change in height from the eave to the peak.
Again, looking at the example above, the eave height is 20 feet. Add 3 feet to that and you get the height at the peak, which would be 23' feet.
If you wanted to measure what the height would be 18 feet from the perimeter of the building, you would divide 18 by 12 and add it to the eave height ( so 18 / 12 = 1.5+20 = 21.5' , or 21' 6" )
Now because the eave height is always measured from the bottom to the top corner of the structure, it's important to know that this only gives you the OUTSIDE HEIGHT of the building.
To determine the inside height of the building, you must subtract out the purlin height. Looking at the example above again, we can determine the height of the purlin by looking at the engineering diagrams (not shown). In this case, our purlins are 8" tall.
So to determine the INSIDE HEIGHT of the steel building, subtract the purlin height (8").
- At the eaves, this building is 20' subtract 8" = 19' 4" interior height
- At the peak, this building is 23' subtract 8" = 22' 4" interior height
- At 18' from the outside wall, this building is 21'6" subtract 8" = 20' 10" interior height
For a single slope building, the calculation is the same except you don't divide the width by 2.
Now it's also important to consider that the main frame support columns that sit under the purlins. So at every Main frame column, you will lose anywhere from 10 inches to 36 inches, depending on the height of the main frame beam, or the "web". Often, if we are planning interior walls in the building, we will position the main frame columns so that they coincide with the interior walls.
It's not possible to know the depth of the main frame column beams until the Metal building engineer has actually designed the structure. There are many factors that can affect the size of the main frame columns, such as:
- height of the building
- distance apart of main frame columns
- snow zone
- ceiling loads
- wind storm zones
- other collateral loads
The depth of the web will usually vary across the width of the building. By tapering the I-beam supports, engineers can put strength where the building experiences the largest structural forces. This strategy minimizes unnecessary steel used in fabrication.
If you want to guess, typically the larger the building, the larger the depth of the main frame columns. I anticipate 12 to 24 inches for building less than 50', and 20 to 36 inches for buildings up to 80' in width.