Flashback time:
One of the most important and beneficial trainings I ever underwent as a young writer was trying to script a comic. I had to cut down all of my dialogue to fit into speech bubbles. I was staring closely at each sentence and striking out any word I could.
“But then I paid for Twitter!”
That seems like an inefficient use of space if the ceiling is anything more than six feet high. If they’re ten foot ceilings, then the shelves are spaced about 20 inches apart, which is rather larger than typical books. No wonder there are multiple layers on some shelves and books overflowing onto other surfaces.