There are interior and exterior wall but there are walls also deferenciate according to loading condition i.e. load bearing wall and non load bearing walls. When load of roof is given on the walls than there design is as load bearing walls, but in case frame structure, when load is given on columns/ pillars than we construct non load bearing walls. In case walls are to take load of roof than external and internal walls are not less than 9'' thickness. In frame structure the external wall should be 9'' thick and internal walls may be 9'' or 4.5'' thick.