Getting back to the core question: “Is sustainable affordable?”
The answer first requires a definition of sustainability—and offers an opportunity to distinguish sustainability from “Green.” A sustainable method or material—or more importantly—a sustainable project, is one that can be produced in a way that does not significantly compromise other’s ability to produce the same thing in the future. It looks forward to our offspring, not yet born. “In every deliberation, we must consider the impact on the seventh generation… even if it requires having skin as thick as the bark of a pine.”
A green method or material—or project—meets a set of standards. It is flooring that comes from rapidly renewable sources, or wood from well managed forests, or a toilet that uses less water per flush. It may be a Passive House project, which uses only so many Btu’s per square foot of floor area. Each of these green attributes contributes to sustainability—but in itself, does not guarantee it.
So sustainability—as a working force—depends on a state of mind, as much as a checklist, or point system, or a certification. Sustainable decisions and actions begin with objective considerations, but since our crystal balls are smudged and cloudy, our judgments must ultimately rely on intuition and faith.
From this point, sustainability must consider two things: the resources that we take from the earth to create our built environment, and to maintain it—and the impact on the natural environment from these creations and activities.
 Attributed to the Great Law of the Iroquois