Hey guys and gals, I have all of my plans in order to build a 10 x 20 shed on an existing slab. I am in need of building 3 scissor trusses and have my pitch set at 12/12 top chord and 10/12 bottom chord. My problem is, how do I know what angles to cut where the two chords meet that sit on the top plate? Also how do I figure the 65" overall height that I need to make sure these match my gables and attic trusses? I appreciate any help yall can give me!

 

Since you only need three it is easy to simply lay the boards out on a level surface and let them lay on top of each other. Then cut through both with a circular saw. If you have a concrete slab already mark out what you need for the truss on the concrete that way you don't need to measure for each one.

You can also do the math. There are also online sites like this that can help with the angles.

 

In a standard joist and rafter attic the bottom chord (the joist) serves to hold the walls together and resist bowing out. Eliminating the bottom chord and going with the scissor design can hold the walls in place IF designed and built correctly. Being built correctly requires more than just the scissor shape.

I'm not an engineer, just a hammer and nail guy with years of experience and here are my concerns.
1. Your lower 10 x 12 chord only provides 1' of web (plus the thickness of your rafter) between lower and upper which will make it very difficult for the scissor layout to actually avoid spreading. There may be some guidance on the internet but my cautions old mind would suggest something like 6 x 12 or less, but best to find a real chart.
2. Assembling a truss with hammer and nails (and glue) can be done, usually with plywood gussets, but care must be taken to hold the pieces tightly in place while you fasten them. Any slack will result in spreading.

Bud

 

Thanks for the reply! I was also suggested to do the same thing on the concrete that you suggested by someone else! I had a guy here at work that is much more advanced in math skills than I am and figured all of the angles for me which was a huge help also! I am going to get one completely cut out and make sure it's correct and then lay each out on the concrete slab that I have! Thanks again!

 

Thanks for the advice here, the only reason I am using the 12/12 the 10/12 scissors is because I had a truss company send me an estimate to build all of my trusses which was about $1000 more than it would cost me in materials to do it myself and they sent me the layout using these pitches. Once I get one cut right and laid out, I am going to put down some scrap 2x4's to lay the truss pieces in tightly before I start installing the webbing.

Would nail plates with screws be better than using the hammer, nails, and glue method? I hear that most people believe this to be a better method for strength over the nail plates.

Also for the spreading effect, I wasn't too concerned with this (with my simple thinking) because I am going to have 2 gable ends and 3 attic trusses on each side for a total of 6 attic trusses and was thinking that this would be enough to keep the walls from bowing even if I went with a simple "A" frame type truss instead of a scissor truss. Not sure I'm correct on this, just thought it sounded like it would work.