An infrared street view shows heat sources in "The Greenest Home: Superinsulated and Passive House Design" (Princeton Architectural Press, $45). ( SG Build photo / May 8, 2013)

The idea of passive house design isn't new. It was first promoted in the early 1990s.

But the concept — virtually airtight buildings, heavily insulated and using triple-glazed windows, requiring little energy for heating or cooling — has yet to capture the public's imagination. Part of the problem may be people's lack of exposure to a passive house. There just aren't that many to visit.

"Unless you can show the public the projects under construction, then stand in it when it's finished, I think it's hard to understand the passive house," says Julie Torres Moskovitz, the founding principal at Fabrica718, an award-winning Brooklyn design firm.

Torres Moskovitz estimates there may be 40,000 certified passive house buildings in the world, but probably fewer than 50 projects in the United States.

"There are also a lot of houses being built with the passive house (concept) in mind that don't quite reach the (certification) level," she says.

The stringent passive house — or Passivhaus — standards and the Passive House Planning Package software were developed by the Passive House Institute in Germany. The U.S.-based Passive House Institute is currently formulating its own standards. The PHPP software incorporates a designer's calculations and helps design a passive house.

A passive house saves up to 90 percent of space heating costs and 75 percent of overall energy costs, though some European studies indicate the numbers may be even higher.

Torres Moskovitz has been waving the passive house banner for several years. She was the project manager on Tighthouse, the first passive house in New York City. Certified by the Passive House Institute in Germany, it's a retrofit of an 1899 brownstone and was completed in 2012. And now she has written "The Greenest Home: Superinsulated and Passive House Design" (Princeton Architectural Press). Even the book fell victim to the public's lack of awareness.

"It took me a while to write the book, and I figured that by the time it came out everyone would be familiar. I thought the title would be 'Passive House,' but the publisher said the public was not familiar enough. So we used it in the subhead. I'm waiting for the idea to hit that tipping point. It's starting to grow. But until (President Barack) Obama speaks about it when he talks about energy efficiency, it's not going to reach the public."

Once it does reach the public, however, it clicks.

She tells about a tour of Tighthouse on a cool, rainy day in October. After the tour was over, she noticed that visitors were just hanging around. The heat hadn't been turned on, but the fresh air ventilators were working, providing constant fresh air — she compares the air quality to a spa. The building was just too comfortable to leave.

There are also misconceptions. People worry about being sealed into a building where the windows don't open (they do). There are fears that the cost is prohibitive (it's only a 3 to 5 percent differential from standard construction, and that is recouped quickly in energy savings). Or there are concerns about radon gas coming up through the earth.

"What we did in our retrofit, which is similar to what they did in Europe, we tore up the existing concrete slab, dug into the soil under the home, installed pipes for drainage, then a new slab was air sealed," says Torres Moskovitz, who studied for a year in Ireland, where radon is an issue. "We had to insulate all around with rigid insulation. Under that is a 15 mil material — like a plastic tarp almost — we wrapped across, went under the slab went up and taped so there could be no leaking."

Consumers interested in passive house design often avail themselves of other energy-saving ideas — rainwater collection or solar power, for example — that fall outside the realm of the passive house. In the long run, that's more savings. But the key is getting people familiar with the concept.

"People learning about it are so into it, maybe it becomes a bottoms-up approach, comes from the public and then the government has to react to our demand," Torres Moskovitz says. "There's definitely interest in the building community, but it has a way to go before everyone understands."