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Just a few weeks before residents start moving into the new Hook & Ladder apartments in northeast Minneapolis, a team of building experts from Chicago is testing one of two buildings for air leaks through doors, windows and unintended passages as landscapers plant bushes and workers sweep up behind the contractors.

So far, they say, it's one of the tightest buildings they've seen, but there's more monitoring and research to be done. The buildings will serve as a demonstration project aimed at showing other developers that it's possible to build an apartment building that uses virtually no energy.

"This is meant to be a testing zone for the industry," said Claire VanderEyk, senior development associate for Newport Midwest, a division of a California company.

Just a year after the 118-unit project was announced, the architects, developer and builder are all eager to see how the building will function once it's occupied. So far, the project has met expectations, they say, but not without a few surprises.

Inside and out, the building that's being tested looks nearly identical to another new one that's across a grassy courtyard, but in many ways the two are dramatically different.

It's the first in the Midwest built to Passive House Institute US (PHIUS) specifications, which aim to make buildings 60 to 85% more energy efficient than conventional guidelines. The second building meets Minnesota Green Communities standards, which provides a road map for developers who want to build green, affordable housing.

From the outside, the buildings are nearly twins. Except for doors and windows, the PHIUS building has only one exterior penetration — a big square louver connected to an 8,900-pound air exchanger that brings fresh air into the building and exhausts stale indoor air. All of the apartments share a single heating and cooling system, which eliminates excess air gaps.

In contrast, the Green Communities building has an air-conditioning and furnace unit in each apartment, so the sides of the building are lined with rows of square metal louvers.

There's another critical difference: The Passive House building has covered parking below a portion of the building instead of a completely enclosed parking garage like the one under the Green Communities building.

Dave Einck, senior project manager for Frerichs Construction, said that forgoing the parking garage makes it easier to manage the building's complicated ventilation system, and by doing without the enclosed garage the developer saved enough money to help offset the 10 to 12% premium for the PHIUS upgrades.

To ready his crews for the project, Frerichs sent a team of contractors to Vermont for a weeklong PHIUS certification course.

The PHIUS building has also been super-insulated, and crews went to great lengths to make sure that all air leaks were sealed. One of the buildings also has a set of photovoltaic panels on its roof that will help produce as much energy as is used by residents, making it a net-zero energy building.

The lead architect on the project, Kim Bretheim of LHB Corp. in Minneapolis, said that all of those upgrades should enable the PHIUS building to use at least one-third less energy than the other one.

Bretheim said while the project stayed within budget, there have been a few surprises. The plan called for triple-paned windows that were only commercially available in Canada, but proved too expensive to use. So the team worked with Iowa-based Pella to design windows that meet the PHIUS standards for the Midwestern climate but will also prevent noise from the nearby trains from being heard in the apartments. Those windows are now available commercially.

"This was a market niche created with a regional vendor," said Bretheim.

Elizabeth Turner, a Passive House consultant and architect with Precipitate, said there was another problem: Traditional ducted clothes dryers don't work in a nearly airtight building, and the specialized dryers that would work were too expensive. So until the cost of those dryers comes down, residents of the PHIUS building will use dryers in the Green Communities building.

In addition to reducing the carbon footprint of apartment buildings, there are financial incentives for developers to build to PHIUS standards. The developer of Hook & Ladder is able to finance the project using low-income housing tax credits that also require energy-efficiency upgrades, so all but 10 of the units will be for renters who earn less than 60% of the area median income.

VanderEyk expects the building to be fully leased by the end of the year and hopes the project will make it easier — and less expensive — for her company and others to build more PHIUS projects..

"As we do more," she said, "the additional costs will balance themselves out."

Jim Buchta • 612-673-7376

Correction: Previous versions of this article misstated where the maker of Pella windows is based.