I have tried several different methods for second floor construction and have found.
1. Although good T&G will work on joist on 4'centers, dirt will work through and show in grooves below. I either put plywood down for carpet or run wood floor perpendicular to T&G.
2. To keep sound at bay, the method described above can be enhanced by adding Sound Attenuation Board or just cork between layers.
3. False floors or 2x floors are good if mechanical space is needed, but are more costly and add to second floor hieght.
4. Make sure structural frame does rest on any built up floor and bears directly to other framing.
