Robert, the floor support has absolutely nothing to do with the
outside style of the structure. The span of joists will be
determined by their load carrying abilities. Flat trusses could
be designed to clear span the 38' in wood or steel. It will
always be a compromise of cost of materials, height clearances,
ease of construction. You don't mention the depth of the joists
in your plans, but I imagine it is done with 2x8 to span 13 feet.
This will always be subject to load requirements, deflection
limits, and span tables.
Keep the whole world singing . . . .
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