The southwestern New Mexico town of Columbus, site of a 1916 raid by Pancho Villa, is now home to a border entry center that is powered by the sun and landscaped with recycled concrete “sponges” that harvest rainwater.

An apartment complex in Los Angeles created expressly for formerly homeless men and women has features that maximize natural light and airflow, a roof designed to minimize heat inside the units during summer, and a rooftop garden that attracts migratory birds.

And across the country in Brooklyn, e-commerce giant Etsy established its headquarters in a 200,000-square-foot building that previously housed a printing press for Jehovah’s Witnesses, then renovated and retrofitted so it is powered by renewable energy.

All three sites, spotlighted last year by the American Institute of Architects in its top-10 list of sustainable projects, reflect the expansive reach of “low-energy” design strategies and the building industry’s embrace of sustainability as a de facto imperative. They’re part of a remarkable evolution, one that could prove crucial since the building sector globally accounts for at least 40 percent of the world’s emissions of carbon dioxide — far more than transportation sources.

Some advocates think the U.S. sector can achieve net-zero emissions within 20 years, a decade ahead of President Biden’s net-zero goal for the country. The administration’s initiative includes new codes and efficiency standards for homes, appliances and commercial buildings — and a clean electric grid. Dozens of cities and states are moving forward with their own measures.

“Decarbonization of the sector is inevitable,” according to Edward Mazria, founder of Architecture 2030, a nonprofit organization based in Santa Fe, N.M., that aims to reconfigure the built environment as part of the solution to global warming.

The past several years served as an “urgent call to action,” he thinks, with devastating storms and wildfires on several continents, profoundly diminished Arctic sea ice, and the highest global temperatures in recorded history. “It’s not a matter of if we transition to renewables, but whether it will be fast and well-orchestrated enough to avert irreversible climate chaos.”

Since the nation’s building stock started its rapid expansion more than two centuries ago, the energy all that construction consumed and the greenhouse gases it then emitted have only increased — dramatically so.

But the numbers began changing in 2005 as building efficiency gained traction. Despite the building sector producing an additional 50 billion square feet in the past 15 years — housing, office parks, skyscrapers, hospitals, factories, schools, shopping centers and other commercial projects — its energy consumption actually dropped 5 percent and emissions fell 30 percent, data from the U.S. Energy Information Administration show.

In Mazria’s view, building “green” is not a hard sell, especially given cost-effective design approaches that can produce high-performance buildings with little to no energy consumption or emissions. Strategies include considering a structure’s shape and orientation on a site, adding “cool” roofs that reflect more sunlight and absorb less heat, and more.

“In 50 years, I’ve never heard a client say they want an inefficient building that costs more to operate and damages the environment,” Mazria said.

Sierra Atilano echoes his sentiment in Los Angeles. She is chief real estate and investment officer for Skid Row Housing Trust, which commissioned the apartment complex in the city’s MacArthur Park neighborhood where formerly homeless people, some of them veterans, now live. Passive design approaches such as the building’s exposure to prevailing winds make it 50 percent more energy efficient than conventionally designed counterparts, according to the architectural firm Brooks + Scarpa.

“Adding sustainability is a no-brainer in developing equitable housing,” Atilano said. “Affordable housing should be designed on par with market rate housing; it’s important not just for the residents but for the community at large — and the environment.”

While new construction is the obvious target for low-energy design, the American Institute of Architects also emphasizes the need to adapt and retrofit existing buildings — an especially salient point given how the pandemic has depressed demand for commercial and office space. The curriculums at the country’s leading architecture schools reflect this reality and the opportunities it offers.

“The median age of commercial buildings in the U.S. is 36, with almost a third of commercial buildings over 50 years old,” noted Erica Cochran Hameen, co-director for the Center for Building Performance and Diagnostics at Carnegie Mellon University’s School of Architecture. “Knowing most of our students after graduation will work on projects that involve an existing building, it is critical to educate them on advanced retrofit and building upgrade design strategies and technologies.”

The results increasingly are quantified. There are benchmarking policies and performance metrics. The 2021 International Energy Conservation Code set new minimum efficiency standards for myriad construction elements, part of “lifecycle accountability” for a building. Jurisdictions that adopt the code’s zero-carbon approach “have an avenue to ask for annual performance data and measure on-site energy generation and off-site energy procurement,” explained Anica Landreneau, sustainable design director for the global firm HOK.

In fact, cities from Portland, Ore., to Portland, Maine, now require such data, and Landreneau sees that as a positive. “Both benchmarking and performance standards trigger retrofits, which create domestic jobs while reducing carbon emissions, increasing energy security and improving quality of life for building occupants,” she said.

Yet home builders have a different take on regulatory mandates, instead supporting “voluntary, above-code programs,” Jaclyn Toole of the National Home Builders Association said. “Maintaining housing affordability must be the cornerstone to any efforts to create greener and more efficient homes.”

And fossil-fuel interests continue to oppose proposals to eliminate natural gas equipment in buildings, successfully pushing legislation in at least 12 states to bar any exclusion. “Policies that would force people to replace natural gas appliances with electric ones could be burdensome to consumers and the economy, have profound impacts and costs on the electric sector and be a very costly approach for a relatively small reduction in emissions,” said Jake Rubin, a spokesman for the American Gas Association.

Environmentalists counter Rubin’s argument by emphasizing the magnitude of what energy improvements achieve in cost savings and decreased emissions — billions of metric tons in this country alone.

“Efforts by gas utilities to fight [building] electrification represent one of the biggest threats facing the planet now,” said Rachel Golden of the Sierra Club, citing a major U.N. report on methane. “Every time a new home or building is connected to the gas system … we’re expanding the use of gas.”

A clear shift seems underway, however. In California, advocates are working to get gas out of new construction through the state energy code. More than 40 cities and counties have already passed measures requiring or encouraging that fossil fuel energy be phased out in favor of building electrification, and the Sierra Club counts more than 50 other jurisdictions in the state that are weighing such policies.

Elsewhere are similar signs of transformation. Burlington, Vt., which became the nation’s first city to go all-renewable after opening a hydroelectric facility in 2014, intends to levy a carbon fee on new buildings that connect “to fossil fuel infrastructure.” In New York City, where a recent, top-to-bottom retrofit of the iconic Empire State Building nearly cut its operational carbon emissions in half, officials are considering a gas phaseout for all new construction.

Legislation is pending in Colorado to support building electrification, establish standards for energy performance and limit emissions from gas utilities. Laws to require or encourage gas-free construction are already on the books in Massachusetts and Washington, the state that is considered the vanguard of the movement.

Kjell Anderson, the director of sustainable design at LMN Architects in Seattle, helped craft that city’s new building code. The regulations, which will phase out gas in new commercial buildings, were a direct response to Seattle’s increased greenhouse emissions between 2016 and 2018.

He predicts emissions will drop each year as buildings go all-electric and the local grid adds more renewable energy. The biggest unknown is the balance required between on-site renewables, the grid and energy storage, which he says calls for region-specific approaches.

“Nearly all ‘net-zero’ buildings generate excess energy on many days, while they draw grid power at other times,” Anderson said. “With the rapid expansion of clean-energy development and the significantly reduced cost of renewables, energy flows both ways, so utilities are becoming energy managers instead of just energy generators.”

Like so many of his colleagues and contemporaries, he thinks the transition to a carbon-neutral economy must be expeditious: “The task at hand is scaling the solution — efficiency, electrification and renewable energy — to the scope and urgency of the climate crisis.”