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Why Can't I Create A Full Truss?

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If you are not already a State Licensed Structural Engineer then why are you wasting time designing trusses? Like many things in software you asked the truss tool to do something beyond its capabilities and in my opinion, beyond your legal rights unless of course if you are an Engineer. Leave Engineering to those licensed and trained to it is my advice or at least work with the software to a useful result and stay within its capabilities,



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Why in the heck are you wanting a upper chord that thick? I'm fairly new to CA and just did my first trusses along with David's help(thank you). It is my understanding of the software that the program tries to calculate truss designs based on the distance between the ceiling and roof planes, if there is not enough as in too thick of an upper chord it cannot calculated it. In most truss designs it is the lower chord that takes the bulk of the span/live/dead load. Most of your load is going into ceiling/floor joist that will need Engineerng more than the trusses, but the I-Beams should do a great job if you use approved span tables or PE. Plus if I am understanding the model you are wanting CA to put a lwr chord/webing through a knee wall? You may want to clarify if you are trying to clear span that truss or take the lwr chord down to the tji/lvl so the guys can help you more. 


David is correct the truss designers have FEM (finite element modeling) I have ran before that lets them know the stresses, once it passes FEM the PE stamps. I have been designing and analyzing(PE) structures and mechanical systems for decades in large corporate and now on my homes. In corporate we ALWAYs as Architects/Designers do preliminary structural concepts as a best design practice as you are and submit to other disciplines. I have two mechanical designs since I am in a design seat right now being reviewed by stress, fatigue, analyst along with many others such as manufacturing/builders, chemist, etc.....


Alot of DIY homes are out in rural with no codes requiring no PE although it is a good idea to design to such. 


I've taken the same approach in my building designs. I first visited a truss company to get a prelim idea of sizing and span. They told me my 50' clear span using their jigs would require a piggy back truss meaning more assembly cost for my spec builds (not a one off) or I need an internal wall/footing more cost. Now I have taken my conceptual truss design to 3 truss suppliers to get the span/pitches/sizing I want and reduce cost. I have made my requirements clear, no piggy backs due to tooling constraints, 2x 6 lower chord minimum for insulation, a energy heel, cantilever, soffits, etc....I have also used the conceptual trusses to get bids from framing trades, give me an idea of additional stick framing reflected in my ML that is out for quote. aid in designing my roof/wall insulation, help me visualize any additional installations such as trays, attic storage, aesthetics, and they allowed me to easily communicate with the truss designers since they wanted dimensions anyway, etc......I can also import the trusses to other programs like FEM/WUFI when I get the software.  If I had to do these trusses again it be very fast and that will only improve in time. IMO you are on the right tract to create the most robust cost effective well communicated designs by modeling conceptual trusses for approval.  

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The reason that you can't build a full width truss is that you don't have enough room to build the truss.

Trusses are built between the roof and ceiling.

You have rooms with ceilings on level 3 with no room for a roof truss.


If you delete the rooms on level 3, there is no problem building a full width truss.

So, do you want rooms on level 3, or do you want a truss?


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