Some types of residential elevators do not use a traditional elevator shaft, machine room, and elevator hoistway. This allows an elevator to be installed where a traditional elevator may not fit, and simplifies installation. The ASME board first approved machine-room-less systems in a revision of the ASME A17.1 in 2007. Machine-room-less elevators have been available commercially since the mid 1990s, however cost and overall size prevented their adoption to the residential elevator market until around 2010.