The instructions say it has to be laid no more than 33%. Does that mean they can’t be stacked?

No. It means just what is says. They can’t be offset more than 33%; stacked is 0%.

I’m curious why you can’t lay it at 50%. I hope to use 8x24 beveled subway tile in my shower.

It is hard for a long tile or a wall to be perfectly flat. Over the whole of 24 inches, it is likely to bow a bit, or your wall to be less than flat. Any deviation from perfect flatness will mean that there will be “ lippage,” where the edge of a tile sticks out more than the edge of the tile next to it. If you lay at a 50% overlap, you get exaggerated effects of alternating rows bowing out in the same place as you go down the wall. Staggering the tiles only 33% will lessen the lippage effect because alternating rows are not the same pattern. Stacking the tile is an even better way to avoid lippage.

Thank you! That makes sense. We love a beveled tile that is 8 x 24 and found a flat (no bevel) as a back up. Which would you recommend? The shower is 6 x 4.5.

I think beveled would be more maintenance because its easier to wipe a flat wall clean.

Beveled tile in our bathroom means that the grout is thicker in certain spots, along every edge and corner. To my eye, it looks lumpy— and is even more noticeable because it’s a contrasting dark grey grout on white subway tiles. Personally, I would never choose that look.