Yukaban (床板) – Plywood structural subfloor used in modern housing construction, typically 28 mm or 30 mm thick. This particular plywood is used directly over beams, and does not require additional joists in a construction method known as “nedaresu” — literally meaning “joistless”. The image below shows yukaban laid directly over the dodai.
One thing to keep in mind though, is that if the yukaban is not tongue and groove (sane), additional beams are required between dodai (ōbiki) to support the yukaban joints. The question may arise as to whether the time spent messing around with additional ōbiki and the associated cost is worth more than the price-difference of non-tongue and groove and tongue and groove.
Admittedly, it’s easier to lay yukaban when it isn’t tongue and groove, as you don’t have to worry about fitting the joints. However, additional dodai aside, there is also the factor of needing to nail considerably more joints when using non-tongue and groove. This difference becomes more and more apparent as the area that is to be laid gets bigger.