Depending on the complexity of your free computational tool it may require you to enter details about rafter spacing usually 16 on center bridge type height and board size.
Truss spacing for metal roof.
I ve had roof truss manufacturers try to convince me it is impossible to place wood trusses at spacings of over every 4 feet.
Most economical when the difference in slope between the top and bottom chords is at least 3 12 or the bottom chord pitch is no more than half the top chord pitch.
With this design change roof trusses could be placed 12 feet apart making it possible for roofs to support the loads to which they would be subjected.
For instance if you are spacing your trusses 18 inches apart make a mark 18 inches from the edge.
These standards are as follows.
As most building these days are using those pre made trusses on the roof 24 inches become the main size for any roofing construction when it comes to its truss installation.
Flat the most economical flat truss for a roof is provided when the depth of the truss in inches is approximately equal to 7 of the span in inches.
This is most likely the standard size that you will find on pre made roof trusses.
Just keep in mind that if the length of the board size is more than 20 feet then you need to use a more expensive type of lvl board and not a traditional pine board for this longer length.
Engineers have since determined however that the physical design of a post frame building will allow for standard spacing as great as 12 feet from the center when using high quality metal connector plates and lumber.
Typical standard the typical standard for the spacing on the roof trusses is 24 inches.
Roof trusses were usually produced on site in the past.