Are structurally separate and independent places of abode. They may: (a) Have been constructed, built, converted or arranged for human habitation, provided that they are not at the time of the census used wholly for other purposes and that, in the case of non-conventional housing units and collective living quarters, they are occupied at the time of the census; or (b) Although not intended for habitation, actually be in use for such a purpose at the time of the census.