It depends on the stairlift model, there are very compact versions, the kind with two or three pipes as guide take some 15-20 cm of the width of the stairs, and

It depends on the stairlift model, there are very compact versions, the kind with two or three pipes as guide take some 15-20 cm of the width of the stairs, and usually (not always) the chair/seat (which is foldable) can be "diverted" laterally. About the 80 cm space required by this Vertiwalk thingy, it is roughly what a mini-elevator would need. There is a (specific) pneumatic mini-lift that is 75 cm diameter: https://www.vacuumelevators.com/home-elevators/ https://www.vacuumelevators.com/home-elevators/ Of course this is not suited for a wheel chair, the passenger must be standing, you need 1,30/1,40 m to be wheelchair accessible.