BOSTON--Among green-building cognoscenti, the Passive House standard is setting a new bar for architects and designers making eco-friendly buildings.

The Passive House concept, which is well established in Europe, is now getting a foothold in the U.S. with a method that promises overall energy savings of about 70 percent overall and a 90 percent lower heating load without on-site solar power.

While the U.S. Green Building's Council's LEED certification touches on energy, water, materials, and location, Passive House, which started in Germany as Passivhaus, brings rigorous requirements focused entirely on building energy efficiency. Because of that focus on lowering building energy demand, some say it yields better performance than LEED on efficiency.

Technische Universitat in Darmstadt, Germany won the Solar Decathlon competition with a Passive House-certified building design.

At a recent symposium on green buildings here, builders and designers explained how they are using Passive House techniques, such as air-tight construction and mechanical ventilation, in a variety of projects, including individual homes and multi-unit residences in the city.

A notably large one is a multi-unit apartment building in South Boston next to a converted 19th-century rum distillery, which aims to be one of the largest to get the Passive House certification in the U.S. The first phase of the project, which could break ground next spring, will have 28 residential units and a few retail locations, followed by a second phase with 65 units.

Following Passive House guidelines typically means about 10 percent higher cost for new buildings, according to the Passive House Institute US. Retrofitting an existing building to be super efficient costs more like 20 percent more than traditional techniques, said Katrin Klingenberg, an architect and the executive director of the Passive House Institute US during the symposium.

The cost difference can be lower, depending on the experience level of consultants and the type of project. With the Distillery, the building's designers focused heavily on the return on investment and project a 5 percent premium, said developer Fred Gordon from Second Street Associates during a presentation. One residential Passive House home in the U.S. came in at 6 percent over market costs, said Klingenberg.

What is it Although it's gaining attention, Passive House is just a blip in the overall U.S. housing industry, and there are few certified consultants. In terms of structures, there have been 13 fully certified buildings, with about 40 in the certification process, Klingenberg said. In Europe, there are some 20,000 certified buildings and market share there is growing.

The approach is beginning to appeal to more in the U.S. green-building scene, including people like Matt Capone, a project director at Nauset Construction, which worked on the preconstruction work of the Distillery project in Boston.

The LEED system works by getting a series of points for promoting sustainability in general. For example, a LEED building can get points for using recycled material or locating near public transportation. Passive House appeals to Capone because it is more quantitative and focused narrowly on energy efficiency.

"What it brings is a measurable system that goes well beyond LEED, something that truly evaluates the building performance at a higher level. There's nothing else like it," he said.

The Passive House concept calls for an air-tight, well insulated building, and a mechanical ventilation system, although a ground-source heat pump is not required. If south-facing walls are available, the building can take advantage of solar heating.

Attaining Passive House certification requires meeting certain energy-efficiency performance thresholds--15 kilowatt-hours per meter square space of living space per year, or 4,755 BTUs per square foot per year. That quantitative, spreadsheet approach doesn't appeal to all designers and has proved to be too stringent in certain areas, according to Alex Wilson, executive editor of BuildingGreen.com and building efficiency expert. But it appeals to many designers because it's an actual, quantifiable standard, Wilson found.

In a talk at the Boston symposium, Wolfgang Feist, who heads the Passivhaus Institut in Germany, said that Passive House follows a few principles, rather than require high-tech materials or fancy energy-monitoring systems. To meet the voluntary standard, buildings should have a very air-tight building "envelope," high levels of insulation, and a heat recovery ventilator that circulates in outdoor air preheated by outgoing indoor air.

"This is not a question of architecture, it's a question of detailing--that's the most crucial thing," Feist said. Mechanical ventilation in an air-tight building ensures that there is very good indoor air quality, he added.

For example, part of the Passive House concept calls for eliminating thermal bridges, or structural components that serve as conduits for heat loss. That means that instead of having a steel beam extend from the building interior to suspend an outside deck, designers need to create a "break," either with insulation or different construction techniques, to stop the heat transfer.

By lowering the energy demand, architects can equip homes with much smaller heating and cooling equipment. Homeowners, meanwhile, benefit from lower bills. The system doesn't impose an architectural style and works for different building types, including standalone homes, row houses, or larger buildings such as schools, adherents say.

Because the Distillery project is larger than an individual home, it is easier to meet the Passive House per-square-foot energy requirements, Capone said. Some products, notably very efficient windows, will likely need to be imported from Germany to meet the requirements, which adds to the cost, he said.

Existing guidelines, such as LEED and EnergyStar, to cut energy consumption in buildings, which account for about 40 percent of energy use in the U.S., will continue and can incorporate some Passive House concepts. In the meantime, the U.S. Passive House Institute, which recently gained a Passive House Alliance advocacy group, is trying to scale up beyond the leading-edge thinkers in green buildings. "Hopefully, we can work together to become a broader solution," Klingenberg said.