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truss equations

Ron Journeau

Ron Journeau

Member
Messages
68
Location
Les Coteaux,Quebec
Finally got the go ahead from the city and swmbo to start the planning stages for my little shop/storage shed.:) Initial building size is 14 x 28, hopefully with a 6/12 slope on the roof. I have been searching for the math needed to calculate the height and length of my trusses, but am not understanding the little I have come up with. If I am understanding this correctly, I should have about a 1 ft. overhang on each side, making my truss length about 16 ft....right? So where do I go to crunch out the height of the peak?:huh: In case you haven't noticed, math is not my strong suit.....but then again, neither is woodworking!:D
 
For a 6/12 slope, with a 16 foot overall width, you'd want the rise to be four feet (48") over the eight foot run (half the truss width), and that'd make the rafters about 8'9½" long.
 
If the bottom cord of your truss is 16 feet. Half of that is 8 feet. you have a 6/12 pitch which means for every 12" in run there is a 6" rise. So 8 feet times 6" = 48" or 4 feet. Now if you have the math skills Jim has you know how to get the third leg of the equation. In theory the math tells you how long the rafter should be. Me I just measure it cause 9 out of 10 times the theory and the real world don't mix.:thumb::rofl::rofl::rofl:
 
When I built the addition to my shop building, a friend suggested contacting a local truss company for a quote. They do trusses for any size structure all the way up to major apartment complexes. I was pleasantly surprised when the quote for professionally engineered trusses was for no more than the materials would have cost me, to say nothing of the time savings. It might be worth checking into in your location.
 
just for the fun of it, i looked for an online truss calculator. i punched in your numbers, and this is what it came up with.

RAFTER LENGTH CALCULATOR

Overhang:1' 0" 0
Span: 14' 0" 0

Your results are as follows:
Units in Feet (Span)= 14
Units in Feet (Overhang)= 1

Slope = 8' 11" 5/16"
 
Dan your math don't agree with Jim"s math:thumb:
See there ya have it my way of just plan measuring bets math every time:thumb::rofl::rofl::rofl:
 
Well i don't know where your numbers are coming from. From looking at Rons first post he is building a 14x 28, not a 16x 28 correct? As far as the 1 ft overhang that don't have a thing to do with figuring the truss size. Your bottom cord will still be 14 ft even if you put a 1 ft overhang or a 3 ft overhang, or no overhang at all. your overhang will come down below your top plate, and then you will kick that back into the main building for your carnish(soffit and facia). So after saying all that your peak will be 42" from the top plate to the top of your truss. If you would like i will draw you up a truss based on the 14 ft width of 14 ft building with all the number you will need to build your own truss. Let me know if you want me to and will be glad to.
Steve
 
It's like this Steve if you don't count that over hang now when you do the math(or just plan measure) your going to think you can get both sides of the truss out of a 16 foot 2x and be sadly mistaken when you realize you can't. So you add it in now buy 10 foot stock cut you 6/12 plumb ridge cut (about 28°) than if you trust Dan's math go down 8' 11 15/16" make your plumb eve cut and you have a rafter. Repeat as many times as necessary (about 16 for this project) join the tops together than cut a 62° angle on both ends of your bottom cord 14 feet apart and install. In theory it will be 42" from the peak to the bottom of the bottom cord in a square line at the center with a one foot overhang on both sides or 16 feet across the bottom of the total truss triangle.:thumb::rofl::rofl::rofl:
 
I hate to confuse Ron more, but the 42" measurement will be from the top plate to the bottom of the rafter at the peak. The calculation using the pitch determines a line, which in Stephen's drawing would be the bottom of the rafter.

Ike
 
jeepers, I never thought that so many of you guys do this for a living, or have been down the path. Many thanks for all the clarifications, and the diagram. Even being so far apart, we may just be able to pull this off...... of course the weak link is me, but now I see that I have some serious backup!
 
Round here they would be about $175 each delivered to your site.:thumb:
One of our suppliers will do the same price delivered to the top of your building about 24" apart. :thumb::thumb: Well they only do it for the guys they know are going to get them nailed down in a timely manner. The rest have to pay a crane fee or have them dropped on the ground.
 
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:thumb:Yeah Bill and Larry, will definitely check out the truss guy, just a few miles down the road, would be kinda slack on my part not to at least ask, as he is right there where I go every day to work. Thanks for the echo and the original post...;)
 
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