Prior to the establishment of senior citizenís retirement homes and nursing facilities, each family took care of their own elderly and/or incapacitated family members. The invalid family member would be given his or her own room, usually on the main floor, at the back of the house.
The invalid room usually had its entrance through the kitchen, possibly so that the feeding of the invalid could be more easily taken care of.
Nowadays most families do not want to be bothered with taking care of their ill or aged family members, so they build houses without setting aside a room just for the purpose of caring for an invalid. It is easy for them to rationalize that they can't care for their invalid family member because they "don't have the room". It is a shame that the Invalid Room is one that we lost over the years.
In the diagram below, the invalid room is indicated in red.