Double L stairs require two 90 degree turns along the flight. They may be used when space is not available for either the straight or L stairs. Double L stairs are not frequently used in residential construction.
U Stairs (dog legged stairs/half turn)
These stairs may be constructed may be either as wide U or narrow U stairs. Both have two flights of steps parallel to each other with a landing between. The difference between wide and narrow U stairs is the space between the two flights. Narrow U stairs have little or no space between the flights while U stairs have a well hole between.