Can you space trusses more than 24" on center if you use 4x4s or 6x6s for the lumber instead of 2x6s?

Question

I'm designing a cabin that will have exposed trusses over the living room / kitchen area. I have a company that will design the trusses for me, but I am expected to provide some amount of indication as to how I want it to all come together.

I don't want standard 2x6 trusses partly because they don't have the final finished look I want, and partially because I don't want to have so many if it's not necessary, again mostly for visual purposes.

The span is 14' from wall to wall, and 31' total length of the room. I live at 8900' where the snow load is 120psf. There are no valleys in the roof at all, it's as simple as can be up there, short of a wood stove chimney pipe coming up through.

I understand that truss strength is more about the depth of the wood (i.e., the 6" vertical of the truss members vs. the 2" horizontal) than the width, but is it reasonable to think that trusses made from 4x4s, 4x6s or 6x6s could be spaced further apart than 24" oc?

This is surprisingly difficult to find on the web, or I'm just not searching for the right thing, so any info or links to more details would be highly appreciated.

Answer 1

Timber frame trusses (and steel frame trusses, for that matter) are frequently spaced wider.

Truss strength comes from the truss design, and the depth of the truss, not so much the depth of the lumber from which the truss is made. My 24 foot span trusses are completely 2x4 material.

Wider spacing means whatever you put between the trusses has to span the wider spacing between trusses while holding the 120 PSF snow load. ONE approach to that is purlins between the trusses and the lower roof sheathing, so the purlins span the trusses and the sheathing only has to span the purlins.

In that environment if you are vaulting the ceiling I hope you've got a plan for venting the vaulted roof...