Homes built before 1900 have decidedly different layouts and amenities than those built from the 1960s to the present. Builders must take into account the legal requirements for escape routes from the bedroom, local codes regarding window measurements and the rules regarding square footage and ceiling height. Builders must comply with industry codes and standards, and real estate brokers must comply with the same standards when listing a property for sale and designating certain rooms as bedrooms.
According to both the New York and California residential building codes, to be considered a legal bedroom, the minimum space allowed is 70 square feet. However, according to the Department of Housing and Urban Development (HUD) that rule only applies if the room is occupied by a single occupant. Sleeping rooms used by more than one person "shall contain at least 50 square feet of floor area for each occupant," according to HUD. The ceiling height requirements hover between 7 feet and 7.5 feet, depending on local ordinances. Check with the nearest International Code Council for your state guidelines.
According to the International Residential Code, a key factor in a sleeping room is safety -- more specifically, the means to egress in the event of a fire or catastrophe. There must be at least two exits in any bedroom, and one of them has to be a an exterior door or window. The International Association of Certified Home Inspectors (InterNACHI) guidelines stipulate that bedroom windows have to open at least 24 inches and must be 20 inches wide for someone to safely escape through them in an emergency. Any burglar bars should have a safety latch that allows it to be disengaged easily from inside the bedroom.
Not every state mandates that a room have a closet to be considered a legitimate bedroom. Homes built before WWII were commonly constructed without closets in the bedrooms, since chifforobes, or armoires, were the norm. In larger cities in particular, it is entirely acceptable to claim a space as a bedroom in apartments that lack ample closet space.
Check local state ordinances before attempting to create bedroom space below ground level. Walk-out or daylight basements must offer the required escape routes via an exterior door or window. Walk-up basements must at least have egress windows that provide ample room to escape in the event of a fire. In Indiana and Maryland, the egress window can be no higher than 44 inches above the floor. Many older homes contain basement windows that are too high to easily access and contain openings too small from which to escape.