Non-plywood subfloor options?

What subfloor options are there for solid wood or other natural materials?

I am planning an addition to my house. Somewhere in the range of 12x30ft. Everything I have ever done either used plywood or already had very old 150+ year old boards on it. Most of the 1x lumber I see these days doesn't seem strong enough for a subfloor. I supposed I could just line it with 2x4 or whatever dimension was cheapest. Are there options specifically for this?

What options have you heard about? What options are available near you?

Hey Mat.
So I’m guessing you have beams as a base?
The necessary thickness would depend on the distance of the beams. Also some insulation would be beneficial depending on your climate and the construction.

Here (dry, warm, southern Spain) we often build on the earth. In that case we like to use gravel, then a slab of limecrete with fiber, then whatever finished floor. Tiles or wooden floor.

Yes, my climate is way too wet and cold to build directly on the ground like that. It will be up off the ground, so I completely agree with adding insulation. The floor support will most likely be 2x10 floor joists spaced 16" on center.

Timber frame construction, which generally has wider spacing between supports like rafters/joists, typically uses 2x6 tongue and groove for decking on roofs, sometimes floors (especially lofts). Pricier than ply, but maybe worth it for certain advantages.