Ever since green building was wrested from the hands of hippies and tucked safely in the technology sector — there are probably more articles about it in Wired than Mother Earth News these days — we’ve been under the impression that the greenest buildings are the newest buildings. Those nifty, skin-thin photovoltaic panels and that high-tech engineered mold-free sheetrock will surely edge you closer to LEED Platinum than some drafty old house with its oil heat and mahogany doors … right?

Not necessarily. In fact, some of our oldest houses are the greenest houses, and Steve Mouzon, the architect who created the Katrina Cottage, is on a campaign to alert homebuilders and homebuyers alike to the inherent greenness of older, traditional American homes; he calls his project Original Green. After all, reusing is the highest in the hierarchy of the three R’s. As Mouzon says, “The greenest brick is the one that’s already in the wall.”

Before the thermostat age, he likes to say, which lets us command internal temperature and climate with a press of a button, “the things we built had to be green, otherwise you simply couldn’t live there.” In hot climates, homes had to naturally cool themselves. In cold climates, they had to trap the heat. And this happened by design, with architectural elements that these days may seem like decoration, but once had form that came from function.

Take, for instance, the kind of architecture Mouzon prefers to reference, French Acadian — or Cajun, as it came to be known in Louisiana. These houses were made of locally found cypress wood, which just happened to be naturally mold-resistant and didn’t rot in the relentlessly hot, wet weather. They had steeply hipped roofs to keep out the hot sun; the roofs hung over long galleries and porches, which promoted air circulation — no AC needed. Another style found in New Orleans, the shotgun, has tall windows that help cool the houses naturally. Cape Cods have centrally located fireplaces and low ceilings to heat efficiently during frigid winters.

Mouzon’s idea is to make houses work like that again, to respect regional differences and make houses that work with the environments in which they sit. “It’s time to put architecture back to work again,” he says. “There really ought to be an architecture that is appropriate to regional climates.”

Of course, you could create a house that works like French Acadian but looks a little more like the Bauhaus, if that’s your architecture of choice, or any of the sleek, glassy towers we associate with advanced green building these days. If you’re building on the Gulf Coast, you want your house to work like a French Acadian, no matter its style — plop a hipped roof down on a brick-faced prairie style, if you must (long as that brick comes from nearby and the prairie-style house has those galleries instead of narrow halls).

“We’re not trying to push old styles,” Mouzon says. “We’re trying to push things that make sense. And it just so happens that things that make sense bear a strong resemblance to the old architecture.”

One other ingredient that makes a house green, an often overlooked ingredient in sustainability: lovability. It can be solar as all get-out, but if you don’t love it, you might be tempted to tear it down and start over. “If a building can’t be loved,” Mouzon says, “it can never be completely green.”

Mouzon hasn’t quite figured out his campaign’s tack. Does he want to retool the building industry, reintroduce regionalism to the community? Or educate homebuyers to understand what might be inherently green about their homes? (LEED 2009 takes regional differences into consideration — more on that in a future column — and groups like EcoBroker can help homeowners find “naturally green” sites.)

His answer: “Both.” Though he has a little more faith in buyers than builders. “Architects,” he says, “are the ones who are least likely to listen.”