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In 2007, conceptualization began for a highly energy-efficient office building as part of a mixed-use development in Milwaukie. Around 12 years later, Northwest Housing Alternatives has a two-story headquarters on track for net-zero-energy certification.

The five-building campus was designed by MWA Architects and built by O’Neill/Walsh Community Builders. Three three-story, wood-framed buildings hold a total of 28 affordable housing units, and another building serves as an emergency shelter. All of those were designed and built to Earth Advantage platinum standards.

But the office building stands out for exceptional sustainability. Project team members discussed the effort on Wednesday during an event held as part of Portland’s second annual Sustainable Building Week. Crews broke ground in summer 2018 and finished roughly one year later. But design work dates back to 2013.

鈥淭he project started with net zero as the goal,鈥� said Bill Lanning, a MWA Architects principal and lead designer for the project. 鈥淓arly in the design it was going to be net-zero ready, but as we moved through design and funds were made available through grants we were able to add the solar.鈥�

That was a huge component, said Afton Walsh, project manager for O’Neill/Walsh Community Builders. PGE provided an especially important grant, Northwest Housing Alternatives Executive Director Trell Anderson added.

鈥淲ith the grant we said, 鈥楬ow much solar can we do?’鈥� Walsh said. 鈥淎nd what is needed for net zero?鈥�

A 38-kilowatt solar array placed on the office building’s roof not only powers that structure but at full capacity is also able to feed power into the campus shelter building.

鈥淭here will never be any power going back into the grid,鈥� Walsh said. 鈥淚t will all be going back into 鈥� the shelter.鈥�

In addition to the solar array, the office building’s envelope played an important role in energy performance.

鈥淲e tend to spend a lot of our love and effort on the envelope,鈥� Walsh said.

Under-slab insulation was used, all sheeting was taped, and an additional air barrier was installed beneath the weather barrier. Meanwhile, the double-ventilated roof assembly features three inches of spray foam under the ceiling sheeting. This gives a final energy efficiency rating of R-69 鈥� far higher than required by Oregon Specialty Code. Finally, vinyl triple glazing is used throughout the building.

Testing showed the building is exceptionally airtight.

鈥淲e did a lower door air test and it came out to .047 (cubic feet per minute) per square foot,鈥� Walsh said. 鈥淲e had to reach 0.1, and we basically cut that in half.鈥�

Lanning and Walsh worked with Green Hammer on the project’s sustainable aspects. The design-build firm has net-zero-energy project experience, especially on the financial side.

鈥淲e talked about budgets and how to set the stage so we could be successful with net zero,鈥� Lanning said. 鈥淩eally, it was looking at how to simplify things as much as possible and focus on the envelope; that’s the first place to start.鈥�

Design started with a passive house model to estimate energy usage. Then the same approach was used for mechanical systems via readily available equipment, including ductless heat pumps and high-efficiency water heaters.

But one of the biggest interior factors was use of a zonal ventilation system.

鈥淭he building is split into four zones for ventilation,鈥� Lanning said. 鈥淎nd with that we used a cross-counter-flow heat recovery system. It isn’t readily used in the U.S. right now, and it has an efficiency of 84 percent, which is much higher than most (energy recovery ventilation) systems.鈥�

Budget constraints led to decisions to forgo other options for ventilation, passive cooling and some automated mechanical systems.

Nevertheless, 鈥渃onstant communication鈥� among team members helped advance the project, Walsh said.

鈥淲e were always verifying,鈥� she said.

That paid off during construction of the office building, when an air gap raised questions.

鈥淲e had started framing and sheeting the roof, and that second gap didn’t make sense to us, so we went back to design team and asked鈥� about it, Walsh said. 鈥淎nd they made changes that meant they were able to give a pretty good credit back to NHA to use on other features. This project was definitely a labor of love 鈥� a lot of hands touched it.鈥�