As a Senior Building, this credit was pretty much a given. We have designed our entire building to be accessible and all of our apartment units to be adaptable, as it is extremely likely that at some point each tenant will need some degree of accessibility. In addition to properly designed floor plans, to accomplish this we install features such as grab bars and adaptable vanities and kitchen countertops and cabinetry.
I'm not sure why the credit specifies showers though. There are many situations where a bathtub is preferable to a shower, and I don't see the need to require one over the other.