[A comfortable tread-to-riser ratio for a six-year-old] In a wheelchair
Half an inch over four feet. Accessibility code dictates anyone in a wheelchair can pass over a threshold 1/4″ tall with another 1/4″ bevel on top (maximum). No stairs. Just ramps and elevators/lifts. Code marks the intersection of law and design, and it can be frustrating terrain. Code outlines intended goals and objectives, and then proceeds to prescribe specific outcomes. If it is too vague, it leaves open loop holes to be exploited. If it is too specific, it makes buildings less useful and less affordable. I’ve heard the term ‘Cubanization’ refer to fears that mandating stricter gas mileage could lead to consumers choosing to keep cheaper older gas guzzlers rather than expensive new cars with better gas mileage.
Historic preservation can be equally strict in its application, including all sorts of exemptions for accessibility codes (i.e. the value of renovating or rehabilitating a historic building is greater than the value of ensuring access for the six year old in a wheelchair). Sometimes buildings are renovated rather than rebuilt in part to get out of modern accessibility code requirements. Design is all about trade offs, but code is determined to strike bright lines in the sand to delineate what can and cannot be built. That said, they have saved the lives of countless people who, in centuries past, would’ve died in tragic and avoidable circumstances in overcrowded and unsafe buildings.