^ Exactly what I was thinking. He said he doesn't heat or cool it though, and I was thinking who heats/cools the crawlspace under the house?
If that was the case, I would also bury the entire system, so the lids are flush mount to the floor, gaining even a few more extra feet.
Heck, I might even keep digging, and discover an entire ancient tunnel network underground, with a lost city, like that one guy in Turkey. Look up man discovers tunnels, and you'll find hundreds of articles of different stories too all around the world.
Imagine finding a cave system under the house, and turning it into a grow bunker?