Even when an entire street was built at the same time and the homes were completed within days of each other by the same builder, the aging-in-place solutions we offer could be vastly different from home-to-home. The way people live in their homes, the way they maintain them, the amount of items they may have collected since they moved in or brought with them from their previous address, any changes or renovations they might already have made since moving in, their individual preference for style and design, and their physical requirements and needs all have a bearing on what we would suggest and implement. Thus no two solutions are likely to be identical although there could be similarities.
This is why there can't be any requirements that we have to meet except for basis construction codes. Even with the placement of electrical outlets, the National Electrical Code (NEC) does not specify how high from the floor outlets need to be (although some local codes might). This is why we see outlets in the kitchen in the backsplash, the end of the cabinet, behind the stove or refrigerator, or near the ceiling for indirect lighting. In large rooms, a floor receptacle is often used.
Door swing, countertop heights, door and cabinet hardware, faucets, mirrors, and many other features that many people like to suggest what should be used generally are not regulated as to what must be installed and used. We are free to appeal to our clients or our professional sense of what works best in a given situation.
Many people like to suggest using a 19" high toilet - the so-called "comfort-height" one. This is desirable for taller individuals and those with hip, back, or knee issues that make siting and rising more difficult. It is not useful for a shorter person or a child. Therefore, it is not a requirement but something that can be used if the situation seems to call for it.
ANSI, ADA, and similar standards are guidelines that can be used if the contractors or their clients want to comply with them, but they are strictly voluntary except where local ordinances require them.
North Carolina State University published in 1997 a list of seven principles for universal design - principles and not requirements. This gives us a great set of design and performance standards to use as we evaluate what exists or what we want to recommend and install, but nothing is required. There are no inspectors to come behind our work to check to see how it was done and that it meets the specifications because there aren't any requirements.
Creating aging-in-place, universal design, visitable, and accessible solutions are very rewarding because they are client-centered and client-specific activities and not anything that is done on a job-by-job basis because there is a mandate or requirement that we do it this way. We get to match our clients needs, preferences, and budget to the space and design requirements and parameters present to skillfully create solutions that appropriate for what will benefit them.