From: "Patrick Rodgers"
Plywood is most likely an odd number of plies but there is 4 ply plywood out
there, and I believe 3 ply in addition to the 5 ply plywood.
The response given was answering a question about UBC Table 23-II-E-2 which
calls for five-ply plywood structural panels. Of course there are other
types of panels.