There are a number of codes related to windows. As windows have been growing in size, and therefore getting closer to the floor, there is a new one that we’re starting to run into.
The International Residential Code section R613.2 Window Sills states:
In dwelling units, where the opening of an operable window is located more than 72 inches (1829 mm) above the finished grade or surface below, the lowest part of the clear opening of the window shall be a minimum of 24 inches (610 mm) above the finished floor of the room in which the window is located. Glazing between the floor and 24 inches (610 mm) shall be fixed or have openings through which a 4-inch-diameter (102 mm) sphere cannot pass.
Basically its saying if your opening is within 2′ of the floor your window can’t open more than 4″. It means paying attention to the hardware ordered for low windows and making sure that egress window openings are at least 24″ above the floor. You can still have fixed windows close to the floor or openings for ventilation only. Anything that needs to open for egress will need to be paired to another window for glazing below 2′.