As an example, say that while we were going to high school there was a requirement that young men had to wear black pants. It could be further required that they had to be a certain type of look and finish such as non-denim. Contrast that with a recommendation or guideline that the pants just had to be a dark color. That leaves plenty of room for individual taste and selection while still following the general idea. Colors could be black, charcoal, navy, dark green, or dark brown, for instance, and still comply with the guideline.
There are plenty of rules that we have to follow in society. They come with consequences for not complying with them. Where we can park our cars and for how long - whether we pay to park there or not - is often specified, with penalties posted for violating those requirements. Speeding and other traffic laws come apply to all drivers as requirements. Notice they are not guidelines, best practices, or recommendations. They are not phrased as it is a good idea to drive less than 65 on the highway to maintain control of the vehicle and be alert to changing road conditions - things that actually are in our best interests. They are phrased as mandates with published penalties for violating these rules.
Back to our aging in place discussion, There are many best practices we can employ in construction that are just good for the client (and for us since we won't need to go back and make repairs). They are sustainable, will not cause maintenance issues later on, and will serve their intended purpose.
Some issues that are phrased as requirements, however, would be much better to view them as guidelines - if we were allowed that option. Complying with building codes is a requirement. We don't get to choose which ones to obey and which ones to ignore.
Conversely, some items (such as grab bars, wall blocking, shower seats, and ramps) generally are not included in the requirements heading but far under guidelines - meaning there are recommended, suggested, or best practices ways to install and locate them. Materials, surfaces, and size of the product often is suggested as well.
When they are required, each location, installation, and basic product design must be the same. This does not account for individual differences in physical size, ability, or decorating sense.
The height of a grab bar in the bathroom for a person less than 5 feet in height as well as one for a person taller than 6 feet would be the same - even though their reach, reach of motion, and general ability to use it could be vastly different. Having a general guideline of where it should be, how long it should extend, and what considerations (height, ability, standing or seated, for instance) might factor into its use would allow us to create solutions that actually served our clients rather than just complying with requirements that they be included.
Colors, surfaces, lighting outputs, glare, shadows, operational handles and controls, and other aspects of the home need to be evaluated on a case-by-case basis for our clients. Where there are guidelines to consider, we can rely on and use them to the extent they are helpful. On the other hand, complying with requirements for size, design, location, color, and other aspects may not fit the specific design needs of our clients because they have to be generalized in order to have wide-spread appeal.