While there are guidelines and standards for design - including ADA - adhering strictly to what is prescribed or suggested might miss or overlook a more comprehensive decision.
The nice thing about residential design is that it is free from following ADA and other guidelines in terms of strictly following them or being held accountable to them. This is why they are viewed as guidelines and not requirements. Often, they are good places to start but then can give way to ideas that seem to work better for individual situations.
With universal design, the seven principles adopted and quantified by North Carolina State University's Center for Universal Design in 1997 serve as the measuring stick for what constitutes effective design, but there are no definitive prescriptions as to which design elements should and should not be employed as long as they fall in line with the essential concepts of the basic principles. Make a case for why something is or is not consistent with these main principles, and go from there.
With that in mind, I suggest using the age and use measuring stick of a first grader and an elderly grandparent to determine whether something is or isn't an appropriate universal design feature. Start with a 5, 6, or 7 year old youngster and see if they can use a particular feature - say a digital thermostat. They can reach it if it is mounted at a reasonable height - generally 48" or less above the floor. They can discern the temperature they see as individual numbers - say a 7 and 8 - even if they don't appreciate what this means in terms of general comfort. They can identify an up and down arrow or button and push it as requested by an adult in the room.
Now, take a 90-year old person - our so-called elderly grandparent. Even using a walker or wheelchair, this person - subject to enough visual acuity to be able to recognize the thermostat when they see it - can also reach it, touch it, and move the temperature setting up or down a few degrees as necessary for their personal comfort.
The digital thermostat serves both ends of the age, reach, and use spectrum and qualifies as a universal design feature or product. In the same intuitive way, other items that we want to consider using and including in the home can be measured and assessed.
We need to ask ourselves in each instance before deciding to include a feature in a particular location if it serves the young and the old, the short and the tall, the seated and the standing, the strong and less strong, and those with different abilities to reach, grasp, and hold various controls or objects. When we are satisfied that most or all people can use something, we can include it. If we discern or conclude that only certain people can use it, then we can include it if they are suitable for the people living in the home and needing to use these items on a regular basis, but we should not conclude that they are universal because they really aren't.
We can start with guidelines and standards, they we can select what to use based on what we feel really works and applies to the widest range of occupants and visitors to a given home or living space.