Having lived mostly among the younger population, and being young myself, I
haven't dealt directly with the issue of alzheimer's/dementia /senility, at
least on a day to day basis.  However, I do conduct the youth outreach for
our church at the state mental hospital.  Caring, helping, ministering to
those that live life with mental illnesses really is about compassion.
There are very few physical design things that can be done that I am aware
of that can help.  Helping people to have access to meaningful physical
activity, like working in the gardens, orchard, helping with community work
projects etc seem to me to be the group side of this, but more important is
the one-on-one interaction and relationship-building that make a difference
- really no different than for everyone.  Physical helps I could see:
sound-proofing, places of retreat to have a time-out when needed, allowing
for animals on the property.  Specifically for alzheimer's/dementia
/senility: icons/pictures in the common house kitchen for where items are
stored, others?
>From my perspective, the social-side has much stronger and effective answers
to these questions.  Reminder phone calls for meals, helping someone back to
their home when they have forgotten where to go and are wandering, etc.
There are no effective physical/material substitutes for caring and helping
others.  Life isn't about having a perfect physical environment, it's about
the relationships we form.