What conduit is used in a residential residence with 15 amp wires?

You need no conduit on a residential home using Romex wiring with wooden studs. For a 15 amp circuit use 14/2 wire with a 15 amp breaker. This can only be used in bedrooms, living rooms, and dining areas. All other areas of the home require 12/2 wiring with a 20 amp breaker.