Help! My pressure treated lumber is warping!
P-T wood is notorious for warping. Unfortunately, there is not much that can be done about it once it warps.
P-T wood is pressure-saturated with liquid chemical in a treating tube, and then allowed to "drip dry" with a very high moisture content. It air drys slowly, depending on the moisture in the air wherever it has been shipped. If it dries out too fast, it tends to warp.
That isn't comforting, but the only thing that you can do is salvage pieces of it that haven't warped and hope to use that somewhere else.