CASE STUDY: PASSIVELY AGGRESSIVE

For its View Haus 5 townhomes in Seattle, well-known builder Cascade Built and award-winning design firm b9 Architects set out with an ambitious goal: to create the city’s first certified Passive House townhome project. Offering striking views of the Cascade Mountains, the five individual and uniquely styled three-story structures are organized around a central courtyard and utilize many of the strategies common in passive-design projects, such as high-performance, south-facing windows and an airtight building envelope.

Yet these strategies are only part of the story. From a systems perspective, constructing homes that meet the rigorous Passive House Institute US standards, now known as PHIUS , presents many additional challenges. One of the greatest potential stumbling blocks is the HVAC system. Combined with the goal of reaching the Passive House standard, the small unit sizes—two-bedroom and three-bedroom homes ranging between 1,100 and 1,700 square feet—meant that HVAC units had to be highly efficient.

Photo courtesy of Aaron Leitz Photography

For the highly energy-efficient housing project, View Haus 5, designed to Passive House standards, the design team employed ductless HVAC systems to improve overall HVAC efficiency and provide personalized comfort control.

Instead of traditional duct-based air conditioning, the architects and Cascade Built reviewed the benefits of a multi-zone, air-source heat pump (ASHP) system. These ductless heat pumps are designed to move refrigerant through small, twin-pipe runs to individual rooms, on demand, where the controlled amounts of refrigerant are then used for conditioning as needed. This means personalized comfort where it is needed, which is improved with the use of electronic smart controls.

For these smaller-scale dwellings, the efficiency and cost-effectiveness of ASHP is readily apparent. Focusing on one of the View Haus 5 buildings, the ASHP system helped Cascade Built achieve a Home Energy Rating System (HERS) index of 47, signifying that this 1,430-square-foot project was more than twice as efficient as the national new home average of 100. And indeed, the estimated annual energy cost for the house is $35 for heating and $28 for cooling, a tenth of the statewide average; overall, the house is 90 percent efficient, say the architects.

Numbers like these are crucial for meeting Passive House standards, and combined with other systems like the LED lighting, the smart specification of an ASHP system made achieving that goal a reality. According to engineers, ASHP systems can also offer striking efficiency benefits compared to more traditional systems, even in larger buildings. New Hampshire’s Hollis Montessori School, for example, used ASHP technology to help realize its goal of becoming the first certified Passive House elementary school in the United States.

Photo courtesy of Eric Roth Photography

Hollis Montessori School in New Hampshire uses ductless and air-source heat pumps to help it become the first certified Passive House elementary school in the United States.

CASE STUDY: MOUNTAINEER’S LIGHT FOOTPRINT

In another first, a Vancouver-based outdoor retailer, Mountain Equipment Co-Op (known widely as MEC), considered even the structural system for its headquarters to be a brand-critical specification. MEC had outgrown its corporate facilities, and the company leadership understood immediately that its new building couldn’t take on just any design expression. Known for its focus on sustainability and renowned as one of Canada’s most progressive retailers, MEC needed the head office to reflect its corporate ethos and provide an example to others as it projected a unique business image. So, what was the design solution? Conceived by architect Hugh Cochlin with Proscenium Architecture Interiors Inc., the four-story, 112,000-square-foot structure is composed mostly of fir and glued-laminated timber columns and beams with nail-laminated timber (NLT) floor decks. It adds up to about 1.35 million board-feet of lumber, instead of steel or concrete.

Photo courtesy of naturally:wood

For the Mountain Equipment Co-Op office building, next-generation lumber and mass timber products contribute considerably to reducing carbon emissions associated with the built environment.

Compared to the cast-in-place concrete systems, the heavy timber structure offered substantial environmental benefits. For one, wood has a much lower carbon footprint than manufactured materials like concrete and, in fact, sequesters carbon from the atmosphere, locking it within for the life of the structure. Across a large building, the impact is significant: The MEC building’s 84,543 cubic feet of lumber and sheathing sequesters 1,726 metric tons of carbon dioxide, and the greenhouse gas emissions avoided by using wood equate to 3,668 metric tons of carbon dioxide—a total potential carbon benefit of 5,393 metric tons.

Using wood presented challenges to the architect and project team, such as detailing the mass timber systems to support static and live loads for such a large structure. With this concern in mind, for the primary structure Cochlin favored the glulam timber post-and-beam system, in which layers of dimensioned timber are bonded together with a structural adhesive. Glulam was a smart choice for the main structure because the great strength and stiffness of the bonds prevents cross-grain shrinkage, a potentially serious issue especially for a building of this size. The nail-laminated timber (NLT) system provided a strong and cost-effective choice for the floors.

The finished building is the largest contemporary wood structure in Vancouver, and it achieved a LEED Platinum certification. More telling, Proscenium’s design has been praised as “stunning” by BCBusiness and as a perfect “distillation of MEC’s corporate culture” by the Toronto Globe and Mail—thanks in no small part to the use of structural wood.