The primary challenge is to create a design that is simple, cost effective, efficient and attractive. It's not an easy challenge and we have loooked to mid-century modern, Frank Lloyd Wright 'Usonian' and Japanese architecture for inspiriation. All updated to take advantage of contemporary materials and technology.
In a sense, our goal is to create a mid-century design for the middle of the 21st century. No one knows what the world will look like in 2040 or 2050 but it's safe to assume that increasing population will place ever greater demands on natural resources, energy and land. A responsible design should use recycled and durable materials wherever practical.
Passive design greatly reduces the need for complex mechanical systems that consume energy, break down and require maintenance. Simplicity contributes to sustainability. This is highlighted in a great graphic from Albert, Righter and Tittman Architects. http://www.alriti.com/sustainability/index.php