Why are Sunlight's highly energy efficient homes smaller than the rest?
When looking closely at the overall impact of various materials and techniques used to increase the energy efficiency of a home, the size of the structure clearly makes one of the largest impacts. If you build a small home, you'll use fewer materials, have lower operational and maintenance costs and impact the land less. Since reducing size has the most impact, it follows that highly energy efficient homes are small.

Why do the smaller homes cost more per square foot?
Small homes, unfortunately, can't reap the benefits of "economies of scale" that larger homes enjoy. Small homes still pay the same for land, utility hook-ups, permits, mechanicals and appliances and a smaller system, in most cases, doesn't cost much less than larger ones. Bathrooms and kitchens are the expensive rooms in any home. Small homes have these rooms too, but don't have as much "empty" (less expensive) space over which to spread these expenses. For example, compare a 1500sf, 2 bedroom home with 2 baths and a kitchen to a 3000sf, 4 bedroom home with 2 baths and a kitchen. While the baths and kitchen might be a little larger in the 4 bedroom home, there is double the overall square footage. Therefore, the cost of the expensive rooms (the kitchen and baths) is spread out over more overall square feet in the larger home, making the cost per square foot less. The overall cost of a small home, however, is less than a larger one.
Designing small homes that really work takes special skill since the designer must make the best use of the space available. The extra time required to think through space requirements in a small home makes design time of small homes similar to that of larger plans.

Can I build a larger, energy efficient, Sunlight home?
You can always build a larger home and you can certainly make it much more energy efficient than standard homes (visit Sunlight Homes for more information.) Some families are large and more space is necessary to accommodate more people. When you divide the number of people by the square footage of a home, you can see that many of the larger homes are actually more efficient per person than small homes for 1 or 2 people. When the number of people in a family is reduced, however, this is the time to look at downsizing.