When I build I plan on T&G all sides of my MDF panels, which will be 4'x4' tiles. I will have visible SS screws in counterbored holes. The screws will hold them down while the T&G will help minimize the effects of humidity and unequal subfloor. The tiles will be chamfered like the ones in the photos above to help minimize any visual error due to any variation in thickness and subfloor error.

At least that is the theory.

Hi - 

Well, I am experiencing some dimensional changes in the floor, as I did not use a T&G type of registry system. I am experiencing some buckling. It is slight, however, and no cause for worry - especially since it is in the kids rooms. After actually installing and living with this floor, I think the best answer for this type of installation is to chamfer the edges and during installation to leave a nail's width of space between adjacent panels. This would look OK because of the chamfer, and give your floor a little bit of room to "breathe". That said, if you cut plugs like I did, you really cannot see them. So, in this case, you could screw every corner AND one midway down the sides, together with the dollop of construction adhesive in the center, and get a pretty sturdy result.

Uncle Ho - 

I think you might consider that if you T&G the sides, you still may get lift if the humidity is high enough to cause the panel to swell if there is no mechanical fastener to hold the panel to the subfloor midway between the corners. One thought - about minimizing panel swell - is to finish all six sides of the MDF before installation and then applying a finish coat to the show side.

 -R.