The first time the player enters Vault 21, it’s a shock to see that nearly all the Vault is filled with concrete. But why did Mr. House fill Vault 21?
Mr. House chose to fill Vault 21 with concrete to turn it into a hotel. He didn’t want guests to wander around to the lower levels, so he filled everything except the top level.
Sarah, a cashier at Vault 21, theorizes that House didn’t want anyone “sneaking around.”
Mr. House chooses to fill Vault 21 with concrete
After entering Vault 21, the player can speak with Sarah, a cashier. She says that although she takes care of the place, it actually belongs to Mr. House.
The player can ask what Mr. House has to do with Vault 21. Sarah says that Mr. House “tried to get us out” before filling the vault with concrete.
She says she helped convince Mr. House to leave the top level of the vault mostly intact. If the player asks about the concrete, Sarah says she doesn’t know. She theorizes, however, that he didn’t want anybody “sneaking around down there.”
The Courier can return to Doc Mitchell in Goodsprings for more information about Vault 21. If the player tells Mitchell that they saw his old vault filled with concrete, he’ll reply.
Mitchell says Mr. House “sure did” fill the vault with concrete. He says House wanted a hotel, and to make sure once he made the change there’d never be any going back. Mitchell says that none of the vault residents had a say.
Just like that, Mitchell says, the residents became homeless and went their separate ways. This vault renovation is part of Mr. House’s future plans for New Vegas.
So that’s the answer. Mr. House chose to fill Vault 21 with concrete to turn it into a hotel. He was worried that customers would explore the lower parts of the vault, so he filled up everything except the top floor.