Large half-layer platform house external additionally-mounted elevator

The invention provides a large half-layer platform house external additionally-mounted elevator. The additionally-mounted elevator is arranged on the outer side of a half layer platform of a staircaseof an old building, and is characterized in that the height of elevator doorway platforms is greater than that of a stair half layer platform by at least 100 mm; non-step walkways between the stairsand the elevator doorway platforms are built on the stairs on one sides of steps with the same height as the elevator doorway platforms, and connect the elevator doorway platforms with the stairs on the floor, and the height of the non-step walkways are greater than that of the stair half layer platforms by at least 100 mm; and new stair steps are additionally built on the stair half layer platforms on the other sides between the stairs, and new stairs extend to the elevator doorway platforms on the floor. The large half-layer platform house external additionally-mounted elevator has the beneficial effects that the hei