If you can apply a hard-headed business perspective to a home purchase, you don’t need a deep understanding of environmental issues to make a decision that is more environmentally benign, said Mathis Wackernagel, the man who devised the Ecological Footprint, a widely used metric for assessing the impact of human activities on the earth’s resources.

Home purchases tend to be very emotional transactions, but when you assume a mind-set of dispassionate, rational self-interest and expand your criteria for decision-making, you’ll create a win-win for yourself as well as the environment, he said in a recent interview.

Beyond the usual “location, location and location” and the size and condition of the house, Wackernagel would add resource constraint. Does the value of the house depend on cheap energy? Will the value crumble if energy prices go up, which they almost certainly will?

The big house with the big yard in a bucolic setting, far from the noise and dirt of the city, is central to the American dream. But, Wackernagel pointed out, if the owner of the big house with the big yard has to spend big bucks on gas to get anywhere, the house will be worth less. If this same owner has to spend a bundle to heat and cool this big house, its value will fall even more.

Climate change will also affect housing value, Wackernagel said. This phenomenon is already bringing more severe weather with colder and stormier winters and hotter summers to much of the country, meaning more heating and air-conditioning energy to stay comfortable and higher household utility bills.

Mathis Wackernagel, the man who devised the Ecological Footprint, a widely used metric for assessing the impact of human activities on the earth’s resources, commutes to work every morning on a tandem bicycle. (Susan Brown/FTWP)

In short, Wackernagel said, “If the value of an asset depends on cheap resources — in this case, cheap energy — it will lose value when those resources become more costly.”

This has already happened in the East Bay area of Northern California, where Wackernagel lives. As recently as three years ago, larger houses with superb views perched in the hills above Berkeley and Oakland commanded premium prices over the smaller houses on the flat. Today, houses on the flat have gained in value while those in the hills have lost it. “People found their car-dependent lifestyle was costing them,” Wackernagel said. Gasoline prices in California are among the highest in the nation.

The cost of living is lower still for a one-car household, as Wackernagel’s is. And this can lead to some unexpected pleasures. He bikes to work every day on a tandem bicycle with his son, who hops off at school. “Without a doubt,” Wackernagel said, “it’s the best part of my day.”

The Ecological Footprint that Wackernagel devised uses an accounting system that converts all the world’s resources — including cropland, grazing pasture, forests, fisheries and the atmosphere — into hectares of land. (One hectare equals 2.47 acres). The Footprint calculation also factors in the size of the ecosystems needed to absorb the waste products produced by human activities.

With all the available resources today and the world’s current population of almost 7 billion, this works out to be 1.8 hectares, or 4.5 acres, per person. People in different countries, however, are consuming resources at vastly different rates. The average size of an American’s Ecological Footprint is 8 hectares, or 20 acres. If everyone lived as Americans do, we would need five planets worth of resources.

In the United States, the biggest and most worrisome part of our collective Ecological Footprint is the carbon emitted as we consume energy, Wackernagel said. The two most obvious ways individuals can make a difference are in housing and transportation. How you get to and from your house to everywhere else in your life is just as important as the house itself.

If you live in a place with good public transportation so that a car is not essential and services like grocery stores are within walking distance, your footprint is already shrinking. If you live in a modestly sized, 2,000-square-foot rowhouse with shared walls, fewer resources are needed to build it, and less energy is required to heat and cool it.

You can reduce the size of your Ecological Footprint further still if you’re willing to live in an apartment building, Wackernagel said. The model he proposed would be based on the Second Empire style and Beaux-Arts apartment buildings that were built along the wide boulevards of Paris more than 100 years ago. These have six floors, which turns out to be the optimal height for an apartment house in terms of cost and energy. Above this height, pumping equipment is required to maintain adequate water pressure to the upper floors. With six stories or less, a hydraulic elevator, which costs far less and consumes far less energy than alternatives, would be adequate. “The single elevator in the old Parisian buildings moves so slowly that most people walk up, and it gives them three more years of life expectancy,” Wackernagel said.

Most Americans would find walking up six flights of stairs unacceptable, regardless of the health benefits. But if this condition were in a building that did in some way conjure the wonder of Paris, and the city where it was built had compelling cultural and social attractions, I would say that real estate developers could still expect a lot of takers.

For more information on the Ecological Footprint, including a tool that lets you calculate your own, go to footprintnetwork.org.

Katherine Salant has an architecture degree from Harvard. A native Washingtonian, she grew up in Fairfax County and now lives in Michigan.