Hi, my name is ***** ***** I've been doing remodel work and building for nearly 20 years, and I can assist you with your question today.
As for a truss that can span 30', yes this is possible.
I don't know, however if it's possible that the support walls of a trailer can support the new beams/ trusses like you have planned.
I would highly recommend that you hire a construction engineer to determine the size of truss(s) you will need. This is because this is one area where you don't want to "get it wrong," because it could weaken the overall infrastructure of the house. (Same applies to the foundation work, and they work together hand-in-hand.) Once you have a rough idea of exactly what you want to do drawn out, the engineer would make a visit to your house to view the proposed new space and tell you the size of the beams/trusses, all figured mathematically. He will also answer your question about a support wall down the center. He will actually have to physically see the space to do this. He will be worth every dime on your project, I promise. Here's an informational article on trusses: http://www.locketruss.com/roofspan.pdf
There obviously has to be support to the structure and where/how you do that will depend on:
1. Your budget.
2. Pre-planning, such as drawing your own blueprint, making sure things are laid out according to scale while it's still on paper, but well before the building begins.
3. Working hand-in-hand with the construction engineer.
4. Understanding the full scope of how the beams/trusses rely on what they are resting on, or what's supporting them.
I'm sure you are aware of the construction methods used to build the walls of a trailer? If not, you might want to search this out on You Tube or google now. It's much different than the methods used to build the walls in a regular house. They are not meant to be substantial for several lifetimes.
Lastly, although you are building where there is no building code in place, trust me, you better search out the largest city in KY, and build according to what is required in that city. The reason? What if you decide to sell the house and then you lose possible buyers because the house doesn't have enough electrical outlets, or the rise on the stair treads are too tall and possible buyers had too hard a time walking up, or you didn't use GFI outlets where you needed to because they were "so expensive," or the foundation wasn't poured deep enough with concrete and in 20 years the house starts caving in, or you were unaware how deep the water pipe was supposed to be laid and it wasn't laid deep enough or in the right way, and then the pipes burst the first winter. I could go on and on, and these are only scenarios, BUT buyers notice these things, and you will too. If you fail to follow code on this or that, it will make possible buyers suspicious of what all was done wrong that they can't see. Building codes are meant to provide safety, comfort, and security to the homeowner. This means you too.
I didn't ask what kind of trailer this was, since there are so many definitions and construction methods used to build the various different forms of "trailers." Please do tell.
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