Remember those heady days when anyone with a 600 credit score and a remote control could nurse their dreams of becoming the next Donald Trump? They’re gone. Remember that market run-up when you couldn’t build them fast enough? Gone.

It’s no longer speculation. According to the National Association of Home Builders, new-home sales dropped 29 percent in 2007, the industry’s biggest drop in four decades. Existing homes haven’t fared any better, with sales figures not seen since 2001 in spite of fire-sale pricing.

Even Home Depot, that old, orange stalwart, posted its first ever quarterly loss last year.

It was quite a party. And what a hangover. The market is glutted with shoddy homes, built or remodeled too quickly, that won’t move. Tour one and you’ll see why. The principal design decision seems to be, “How can we get the most dollars out of this joint as quickly as possible and get to the next one ahead of the crash”?

It’s a grim situation, to be sure, but all is not lost. One market segment continues to rise, seemingly unaffected by wild corrective swings. Homes built or remodeled “green” are still in high demand and every smart builder or developer in the country is pushing in that direction.

Oddly, people are willing to pay a premium for homes that appeal to an environmental or ecological ethos, even in the current buyer’s market. Marketing hype, you say? Passing fad? Perhaps.

Or, just maybe, it’s because green homes, new or remodeled, are conceived, designed and built with a focus on the occupants, not on the investor.

A house, any house, is a system of interconnected parts. What makes a house green is a focused effort to integrate all those parts to make the most of this house-as-system concept. Four basic criteria for house-as-system are: