Carly Coulson went to a prestigious design school in ­Chicago, won an international fellowship and worked for a top-shelf architecture firm in London, which put her within exploration range of the French Alps.

Spending time in the mountains helped her reconnect with nature and solidified her resolve to live and work amid the rugged boreal forests that skirt the rocky North Shore of Lake Superior.

So after the Waconia native moved back to the Twin Cities and worked on several major commissions, she moved to Duluth and worked for nearly a decade with David Salmela, an architect known for his breakout designs.

In the North Country, she found herself in the company of like-minded architects and designers who embraced a set of international energy efficiency and sustainability building standards called Passive House. She quickly came to realize that there was a way to design buildings that met — or exceeded — those Passive House standards without compromising the design of the building.

"We want sustainability to be invisible," she said. "Is it a green building? No one can tell, and we won't need points or plaques."

She calls her approach Invisible Sustainability and she's designing buildings that use little or no energy, even in frigid climes.

The catalyst for that innovation was a project called the Disappear Retreat, a compact getaway in the woods that uses less electricity than a single light bulb, even in the most harsh winter conditions.

"The defining aspect of that project is that it pushes the boundaries of dissolving sustainable elements beyond anything I've done before," Coulson said. "On these wonderful subzero days, I get especially excited about our 'North' climate because we are producing buildings that require no mechanical heating. Minus-40-degree Fahrenheit — not a problem!"

She said that discussing the Disappear Retreat with other clients and other architects challenged her to find a concise and inspiring term to describe her approach. In this case, "invisible" refers to many factors, ranging from design strategies to the integration of components that are actually visible.

Coulson is able to achieve a 70 to 80 percent reduction in the energy consumption of a building using simple, low-tech strategies. That includes super-insulating and super-sealing a compact building envelope and designing the building to take advantage of passive solar heating and summer shading. All of it can be done, she said, by seamlessly integrating those features into the architecture.

The technology that makes buildings energy independent in a sustainable way, including photo­voltaic panels attached to the roof and wind turbines in the yard, has been available for decades, but shifting political views on the topic of climate change have only made the approach more relevant, she said, and strengthened her resolve to make such concepts more mainstream by doing more lectures and spreading the word about her ideas. "I came to realize that Invisible Sustainability can have a bigger audience and market," she said.

She's also working on MH House, a four-unit home and office development on the central hillside of downtown Duluth. The design calls for reducing energy consumption by 90 percent without using any renewable energy. The entire project will have a peak heating load of only 2000 watts, the energy consumption equivalent of a single hair dryer.

Ken Levenson, director and board member of the North American Passive House Network and the chief operating officer of the Brooklyn, N.Y.-based 475 High Performance Building Supply company, said that Coulson's work is unique both technically and aesthetically. Too often, he said, elements that make a project more sustainable and energy efficient are an afterthought and a visual distraction in the design process.

"It's not like solar panels where you can show them off so that everyone knows you're green," Levenson said. "The goal is to make it look normal."

Levenson said that by promoting the concept of Invisible Sustainability to her clients and fellow architects, and by implementing the idea in building projects that have already moved beyond the drawing board, Coulson is breaking new ground.

"It's a brilliant term and I think it's almost an aspirational goal," he said. "She's pushing the limits of how architects and their clients think about it."

Jim Buchta • 612-673-7376