Passive House certification in cold climates

Prefinished metal siding on south and east elevations.
Prefinished metal siding on south and east elevations.

In cold climates, the standard aims to “reduce peak heating loads to facilitate the provision of high comfort levels with simple and reliable mechanical systems” (For more, see “Passive House: Information for Property Developers, Contractors, and Clients,” published by the Passive House Institute [PHI] in 2014.). The thermal performance requirements of the standard allow a building to maintain a comfortable indoor temperature year-round while using less than 15 kWh annually to heat or cool 1 m2 (10 sf) of useable space, limiting primary energy use for the structure’s full operation.

This reduction of primary energy use facilitates the transition to net zero by decreasing the amount of energy produced onsite. Further, due to the ‘passive’ nature of the Passive House standard, components are adapted to local conditions, so buildings can maintain interior temperatures for days without power. When it comes to resilience and durability, Passive House-certified buildings provide a responsible use of capital dollars. Saving on operational costs across the total life expectancy of a building, the standard allows taxes to be directed to more relevant priorities, such as social programs.

In 2015, the process of evaluating the construction of Valleyview’s new town hall began. After completing a preliminary design, the town opened the bidding process for a design-build contract for a Passive House building at a competitive price, which controlled the possible cost overruns innovative technologies often require. In 2017, the design-build contract was awarded to Scott Builders and the team of designers and consultants it hired (mentioned earlier in this article).

The combination of orientation, fenestration, and building envelope systems is key to effectively maintaining comfortable indoor temperatures year-round.
The combination of orientation, fenestration, and building envelope systems is key to effectively maintaining comfortable indoor temperatures year-round.

Adhering to the standard’s requirements, Flechas Architecture designed the Valleyview Town Hall  by following key principles of flexibility, functionality, accessibility, comfort, and sustainability. These values allowed the team to overcome various challenges faced during the design services, permit, and construction phases of the project.

In northern climates, site placement and design optimization are extremely important, and even more so when it comes to the Passive House standard, as controlled solar gains help compensate for the regular energy losses of the envelope. Due to the extreme cold temperatures experienced in Valleyview in the winter, having a large site with a long side facing south allowed the team to capitalize on sunlight exposure and the necessary heat gains. Here, the configuration of the 2773-m2 (29,848-sf) site was perfect to accommodate the owner’s statement of requirements as provided by the town and fulfill the requirements of the standard. Meeting the Passive House standard in such a cold climate and on a site with little sun exposure would have been difficult, if not impossible, otherwise.

The relationship between the building form and window configuration plays a seminal role in achieving Passive House certification. On this project, meeting the standard’s requirement for space heating of 15 kWh/m2 per year necessitated additional attention to the energy performance of the building envelope. For this reason, careful design considerations were made regarding sun exposure and fenestration needs.

With the main entrance located on the west side of the lot, the rectangular massing extends eastward and exposes the long side of the building to the south, where all high-traffic working areas are located, maximizing the benefits of natural light in the workplace and providing views of the green area south of the building. The building’s orientation and simple layout are designed to achieve the optimal levels of sun exposure required to heat the building in the winter, helping maintain comfort indoors even when it is freezing outside.

Sun exposure also posed a challenge in the longest and warmest days of the summer, as the project team then needed to reduce heat gains and ensure steady and comfortable indoor temperatures without compromising spatial flexibility. To ensure both energy efficiency and controlled natural light, as well as manage heat loss, Passive House-certified windows with a G-value of 0.57 were specified. This means the windows corresponded to a gain of 57 per cent of the inwardly radiating energy. The size and spacing of the windows was carefully considered to accommodate future changes to the functional layout throughout the extended lifespan of the building. Ultimately, fixed exterior solar shades measuring 914 mm (36 in.) were specified above all south-facing windows to control sunlight and potential heat gains in the summer months.

Due to local unavailability of commercial Passive House-certified door systems compatible with common commercial hardware, it was necessary to specify light commercial doors. Regular commercial doors are compatible with many types of hardware, including automated closers, card readers, and panic bars. Most of these doors, however, perform badly when it comes to energy efficiency and air infiltration due to poor details at unit construction, latching, and accessible thresholds. This substitution was only possible due to the small occupancy of the structure (a Part 9 rather than Part 3 building under the Alberta Building Code [ABC]).

Despite the advantages provided by the site’s orientation and fenestration considerations, the extreme winter climate conditions remained a serious challenge, as maintaining a steady indoor temperature of 20 C (68 F) while it is –40 C (–40 F) outside demands more energy than permitted under the Passive House standard. In cold areas, insulation of the whole building envelope, high levels of airtightness, and efficient frost-protection strategies are crucial to keep the interior warm in the winter without an active heating element like a boiler or furnace.

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