Stairlifts can be fit to most staircases. However, staircases need to be wide enough so that those riding in a stairlift do not hurt themselves by hitting against the opposing wall and others do not trip over the stairlift while navigating the staircase. Vertical height may also be a limiting factor for perch seats, where the user requires more vertical clearance. Those with curved staircases will require customized stairlifts, though several companies can accommodate complex multi-level and even spiral staircases.