Jim's link to the judo floor article pretty decent. However, there is one long-term issue that many (including the judo floor) designs do not take into consideration. Over time, the movement of the floor, mats, wood, students, etc. will cause screws to back out and/or break. Not good if you take a breakfall on a screw that has backed out up under the mat. best bet is to create a floor system that does not use any fasteners. We used 3/4" tongue and groove OSB (or plywood) and foam blocks (like the judo guys) only we made ours from sheet foam and used 3 different sizes. Basically we did the following:
1. Lay out floor so that all joints are staggered. Which means that, depending on your floor size, you will have half/partial sheets on one/both ends of each ply/OSB run.
2. use 2' center spacing for the foam blocks and cut the foam blocks based on where they are in the layout - 6"x6" for blocks in the 'field' of each sheet, 6"x12" blocks to cross the seams of 2 sheets of ply, and 12"x12" blocks wherever there is an intersection of 3 sheets of ply.
3. glue the blocks with contact cement to the plywood sheets. for blocks that straddle a seam, glue the block to the first sheet that goes down and let the other half of the block 'float' under the sheet in the next run.
4. Make sure you allow for expansion with your perimeter frame since the wood will expand and contract due to seasonal temperature/humidity variations (I used 3/4")
I used 1-1/4" closed cell foam to make the blocks (www.resilite.com
) and for my foam on top of the floor (my mat is covered with canvas). my perimeter frame is doubled up 2x4s which give the perfect thickness to match with 2 layers of foam and the 3/4' ply thickness. When I designed the floor, I took into account the eventual switch to tatami, so dimensionally, the tatami will fit as is. All I have to do is remove the canvas and foam and then replace with tatami.
Make sure that if you are putting the mat on concrete, you either seal the concrete floor, or lay down a vapor barrier. Otherwise, you will get moisture buildup over time and may end up with a mold /mildew issue on the underside of everything.