In a nutshell, it's the shell: Everything that separates and protects indoors from out-including exterior walls, insulation, roofing, foundation and flooring, windows, and doors.
It's not easy being all things to all people. Those who take this approach to design, however, give it their best shot. Universal design addresses the needs of people at all levels of physical ability in the design of buildings and products. A building that is accessible to the disabled, without requiring special adaptation, is an example. So is a home that anticipates the way owners will use it differently as they age. Also referred to as inclusive design.