Incredibly, there are now companies that make shaftless, retrofittable elevators designed for domestic use.
For wheelchair users and people with mobility issues, this type of elevator provides a relatively affordable way to provide stair-free access between two floors, with vastly reduced construction costs versus adding a conventional elevator and shaft (if your local building codes would even allow that).
One such model is the Stiltz Trio Alta, which runs about $35,000, uninstalled. Zack of JerryRigEverything, whose wife Cambry is a wheelchair user, purchased one. To save some money on the installation, he DIY'ed it with a couple of guys. Admittedly I can't tell if they're buddies or contractors, but Zack did more than his fair share of the work, and as always, made it look easy:
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All told, it took the three guys "about 2 days for the construction and framing, and another 2 days for the lift assembly," Zack writes. "But I think it turned out pretty cool." Agreed!