Complex sentence: Knee walls are common in old houses that are typically not a full two stories in height, in which the ceiling on the second floor slopes down on one or more sides.Kneewalls are sometimes referred to as one and a half stories.
Split into simpler sentences: Knee walls are common in old houses that are typically not a full two stories in height, in which the ceiling on the second floor slopes down on one or more sides. These houses are sometimes referred to as one and a half stories.