There are a total of 23 available room types that when built begin at level 1 and can be upgraded with caps to a maximum of level 3. Rooms can also be merged up to three times by placing an identical room of the same tier next to it. Generally, each room can facilitate two dwellers. Merged rooms may be occupied by up to 6 dwellers. Production rooms require a specific S.P.E.C.I.A.L trait to run, while training rooms increase a specific trait of the selected dwellers. Production rooms can also rush production.