Additionally-mounted elevator capable of saving outside-building ground and directly reaching original gates of residents

The invention provides an additionally-mounted elevator capable of saving the outside-building ground and directly reaching original gates of residents. The additionally-mounted elevator is arranged on the outer side of the position of an old building semi-layer platform, at least partial elevator door platforms are arranged in the old building, step-free ramp walkways are inclined upwards from the elevator door platforms to gate platforms, the slope ratio is smaller than 15%, steel bars are inserted into side beams and stair side wall holes which extend out of middle columns at the same time,cross beams supporting the step-free ramp walkways are formed by pouring, and an elevator is provided with double-doors with inner doors and outer doors capable of being opened and closed. The additionally-mounted elevator has the advantages that the occupation of the outside space of the building is reduced, and can meet the requirements of a government for the environment specification of the distance between two build