These days, many of us are trying to meet two seemingly conflicting goals: We want to build the finest housing possible, but we also want to make that housing available to people other than the wealthy. In 2007, the company I co-founded many years ago - South Mountain Co., on the island of Martha's Vineyard, Mass. - was given an opportunity to pursue those goals when we were chosen to design and build a neighborhood of eight two- and three-bedroom Cape Cod–style homes. The property - which was designated affordable housing - was part of a 26-acre purchase by a...