Egress windows are required in habitable basements as an emergency exit in case of fire or other such disaster. If a basement is divided into sleeping quarters or bedrooms, it must have an egress window for each room. This can be either an actual window, a skylight, or a door, but it must meet specific requirements. According to the International Building Code, basements and sleeping rooms below the fourth floor must have windows that meet the following measurements, among others:
They must be at least 24 inches high and and at least 20 inches wide.
The bottom of the window must be within 44 inches from the floor.
It must open from the inside without tools or keys.
Note that the window must have a net square opening (the space once the window is open) of 5.7 square feet, or 5 square feet for a ground window. These measurements should be the actual square space a person has to climb through, set to accommodate a firefighter in their gear with or without a ladder. (A window with the above dimensions of 24 inches high and 20 inches wide must actually be larger in one direction or the other to accommodate the net square opening number, hence the phrase at least.)
Most newer construction should provide appropriate egress windows in each sleeping quarter, but older homes and those with remodels are difficult to monitor. Make sure each sleeping room in your home has an escape route in the form of an egress window. Contact your local building codes for specific requirements.