james t kirk,
The roof of our house uses a toothpick type of construction (the roof structure is not prefab). The ceiling joists are all 2x10s as are the roof joists. The 2x4's I put down all span over multiple walls including the main bearing walls. Also, we don't plan on storing anything very heavy. I'm sure the new floor will support the load. If not, I'll post it here!
Thanks for your info.