How to add horizontal pane above vertical panes in tmux?

Question

I remember doing this before, but it was pretty tricky and I can't quite remember the combination of commands to get it to work. How can I turn my window with two vertical panes:

+------------+------------+
|            |            |
|            |            |
|            |            |
|            |            |
|            |            |
|            |            |
|            |            |
|            |            |
|            |            |
|            |            |
|            |            |
|            |            |
|            |            |
|            |            |
|            |            |
+------------+------------+

Into a window with one horizontal pane and two vertical panes in an orientation like so:

+-------------------------+
|                         |
|                         |
|                         |
|                         |
|                         |
|                         |
|                         |
+------------+------------+
|            |            |
|            |            |
|            |            |
|            |            |
|            |            |
|            |            |
|            |            |
+------------+------------+

Answer 1

Think I may have figured this out based off of this question. This specific layout is the third in speakr's answer (C-b M-3). Last time I did it in a much stranger way.

Answer 2

You can simply split one of your panels and rotate between layouts with "C-b Space". For some reason "C-b M-3" is not working properly on my computer.