The first novel in the trilogy is Wool (2012). Why wool? Because capital punishment involves sending condemned prisoners out of the silo to clean the few windows with a wool cloth before the poisoned environment kills them. And the windows often need cleaning, it seems.
Another way of keeping down the population is to have a lottery. the winners being permitted to have a child.
Howey kills off one main character after another in the early chapters, and so when Juliette is sentenced to a cleaning we don't know if she will survive or not. But she survives long enough to discover another silo and eventually inspire a better future for her home silo.
The silo goes down 144 floors, meaning that characters must constantly climb or descend using the tiring staircases. There are no elevators. Juliette works way down in the mechanical area when she is chosen as the new sheriff of the silo. The man who thinks he should be the one actually running the silo objects to her selection, leading to her being sent out to clean.
The people of the silo know nothing of past civilizations before the silo was built. Horses and elephants seem mythical to them. They don't even know that there are 49 other silos, at least until Juliette finds one of them. War there has left few survivors, and war threatens her home silo as well. Can she save either or both silos?
Wool is first-rate science fiction, both a great story and an intriguing imagining of a possible future.