While a brownstone can also be referred to as a row home, the term usually refers to a specific architectural form and building material. In contrast, row houses in Philadelphia are commonly defined as any single-family property that links to other similarly sized and designed residences that are lined up along a city block. However, this definition has become somewhat blurred over time due to the increasing popularity of attached townhouses and multiunit buildings that feature similar floor plans. The main difference between brownstones and row homes is their construction. Brownstones are generally built from stone or brick and often have wooden floors. Row homes are typically constructed from wood frame with plaster or vinyl siding and sometimes have concrete foundations. The interior design of both types of properties tends to be very similar with just a few minor differences such as the presence of brick or stone walls and ceilings, hardwood instead of carpeting, and aluminum rather than steel roofing materials. Although both brownstones and row homes are considered single-family dwellings, they function differently when it comes to renting out rooms or units. For example, brownstones are usually divided into one large room that serves as the living space and another smaller room that is used for sleeping. In addition, brownstones usually have stoops or front steps where people could leave messages for each other or pets could be let out of their cages. These areas are called "lobbies" and they provide a place for social interaction outside of the family unit.