The picture associated with this post shows the joining we used to connect our 6 x 6 timbers as well as the angle bracing we employed. The beams are all oak and the angle braces are Cherry from a tree that my wife and I timbered this Winter. For the environmentally concerned, the tree was standing dead. It was killed by invasive English Ivy planted on an old city lot. The house long ago burned though the landscape plants survived and spread unchecked to kill over forty trees. Much of this house is constructed of those unfortunate trees. The poplar subfloor, the cherry bracing, the pear roof purlins are all a direct result of some 1920s city dweller planting a tiny little English Ivy plant. I am not sure whether to be grateful for the lumber or remorseful for the lose of mountainside forest.
Back on topic, The upstairs floor is supported by oak 4x4 beams resting atop the 6 x 6 beams. The space created between would be excellent for storing dust bunnies but we plan to use the space atop the beams for recessed lighting. Depending on conditions once we move into the house we may run one inch ridged foam in the space to to dampen sound transfer between floors. Lets be honest its 400 square feet foam or not there is going to be sound transfer. The other thing the gap above the 6 x 6 beams affords us is the ability to run a couple of low profile air ducts. Currently we do not plan to run A/C but if the day comes that we do desire a flush of icy air in mid August then we will be prepared to run the duct work. Once all of these things are completed; wiring, duct work, foam, we will install a vice wood plank ceiling. We will not be using any drywall in the construction of this house or at least that is the plan. We will have painted wood walls, stained walls, concrete walls but no drywall. It is a small enough space to cover that we thought we would forgo the easy and normal and opt for something different.