Active Thoughts on Passive Design: Designing with wood for next-level green projects

by Katie Daniel | July 12, 2016 1:27 pm

By Peter Moonen and Lydia Hunter
Shortly after the energy crisis of the early 1970s, a group of researchers from the National Research Council of Canada (NRC) and Saskatchewan institutions, led by Harold Orr, set out to transform how buildings were designed and constructed in this country. The result was Saskatchewan Conservation House—a forerunner of today’s Passive House (PH) projects. (These groups included Saskatchewan Research Council (SRC), Saskatchewan Housing Corporation, Saskatchewan Power Corporation, the University of Regina, and the University of Saskatchewan).

The Saskatchewan House employed the basic building blocks of PH standards—compact and efficient design that aimed to minimize the amount of exterior surface area per floor space, informed solar orientation and shading, superinsulation, attention to airtightness, and the installation of one of the world’s first heat-recovery ventilation units. At the time, the house was coined the most airtight building in the world with a blower door test result of 0.5 air changes per hour (ach) at 50 Pa (1 psf).

The Saskatchewan House started a revolution in Canadian construction; it has been credited with initiating the R2000 program. Still, the design principles did not universally catch on with the country’s codes and building practices. (The reasons for this range from crashing oil prices to the fact it represented such a major leap in code and costs from that period’s conventional construction. Further, many North Americans were taking a shorter-term approach in how they viewed the lifespan of their homes). However, the project was studied by two physicists in Europe who, faced with significantly higher energy costs, refined the design process, lead to the Passivhaus concept.

Understanding Passive House
When many people think about ‘Passive House,’ there is often confusion that it is purely a European concept with only nominal relevance in North America. However, this is not the case, as is illustrated by the increasing number of developers, designers, builders, and owners opting for this better way of building.

The confusion around the concept can be forgiven—after all, even the phrase ‘Passive House’ is misleading, explains Rob Bernhardt of Canadian Passive House Institute (CanPHI) West. (At publication time, CanPHI West was poised to undergo a vote to change its name to ‘Passive House Canada—Maison Passive Canada; It is an affiliate of the International Passive House Association [iPHA]).

“Neither word accurately reflects what a Passive House building is,” he says.

Indeed, while most PH buildings use passive solar gain to heat in winter, the building is anything but passive. Air is intensely exchanged for fresh air while high-performing heat recovery systems capture thermal energy. Consistent comfort and air quality are paramount.

Additionally, the concept is not just for residential projects. Today’s PH buildings demonstrate that beauty, comfort, and healthy living are eminently compatible with environmental stewardship and the economics of buildings. As well, the design practices are effective in schools, commercial, retail, and office buildings, as well as multi- and single-family homes. There is even an 80-m (260-ft) high passive office tower in Vienna, which ironically sits on the site of the former OPEC headquarters.

The Passive House standard is an international, performance-based building standard that focuses on dramatically reducing the energy required to achieve a comfortable temperature year round. The following criteria must be met:

• space heating demand: heating and cooling not to exceed 15 kWh/(m²a) or the heating/cooling load is limited to 10 W/m² (peak demand);
• primary energy demand: conventional primary energy not to exceed 120 kWh/(m²a) for all domestic applications;
• airtightness: air changes being limited to 0.6 ach at 50 Pa (1 psf) pressure; and
• thermal comfort: during the summer, excessive temperatures (i.e. >25 C [77 F]) may not occur more than 10 per cent of the time.

Achieving these points is possible through efficient design that utilizes passive heating and cooling techniques and an optimized building envelope that is airtight, super-insulated, and fitted with energy-efficient windows and a heat-recovery ventilation system (HRV).

As is the case for the Canada Green Building Council’s (CaGBC’s) Leadership in Energy and Environmental Design (LEED), Passive House is a certification program aimed at reducing the built environment’s impact. However, the two systems have different approaches. The latter puts greater emphasis on absolute metrics around energy use and is not based on accumulating points. A building either can or cannot meet the stringent metrics for energy use, comfort consistency, and air changes.

Products (i.e. Certified PH Components), designers (i.e. Certified PH Designers), tradespeople (i.e. Certified PH Tradesperson), and projects can all be certified by affiliates of the International Passive House Association (iPHA). There is a product database online[1], but non-certified components can be used in construction as long as the thermal performance is modelled.

Designing with wood
A passive design building can be built using any of the major structural materials—wood, steel, or concrete. Most smaller buildings, however, tend to use wood products if the prevailing code permits. There are many reasons for this.

Since energy efficiency is a driving concern, great efforts are made to reduce the impact of heat loss through thermal bridges. Wood transfers thermal energy at a much lower rate than either steel or concrete. This in turn reduces the amount of time, labour, and materials required to offset thermal transfer associated with other materials.

As a material, wood can also be machined to extremely tight tolerances. Since many PH buildings are fabricated in panels, components, or volumetric units, precision assembly is important to avoid any air leaks—and the energy and moisture therein. Further, wood has a low mass when compared with other structural materials. Reducing the mass of transport for prefabricated elements has both environmental and cost savings. Other sustainability-related implications include the fact wood is renewable, sequesters carbon, and has a lower embodied energy than other traditional structural materials.

PH in Europe… and Canada
Energy performance is increasingly being incorporated into building codes around the world. More than 50 jurisdictions in Europe either require or reward buildings built to a ‘passive’ level. The metrics for certification of a PH building are the same globally, with projects certified in severe cold and hot/humid climates. (For an international database of PH projects, visit www.passivhausprojekte.de/index.php?lang=en[2]). However, in the United States, there has been vigorous debate on the merits of having adaptable standards to reflect different climate regions. This would result in variable performance levels depending on location.

In Vorarlberg, Austria, PH design is a requirement for all social and affordable housing projects. The rationale is the occupants of these buildings are least able to afford the high energy costs associated with imported natural gas and fossil-generated electricity. Social and environmental aspirations mesh seamlessly with economic considerations.

In 2008, the European Union passed a resolution calling on each European member state to adopt the Passive House Standard by 2016 for all new construction and major renovation projects. Ultimately, this resolution will alter the construction industry in all parts of Europe, as the continent recognizes the need to build for long-term economic benefits, improved indoor air quality (IAQ), and personal and national energy security.

Uber-high-energy-performance building culture may well have been refined in Europe over the past 20 years, but it has firm roots in Canada. Now, it appears those roots are bearing fruit with a number of projects being certified across the country. (To see a listing on CanPHI projects, visit canphi.ca/our-resources/projects[3]). Passive House is gaining ground in Canada as an ambitious, but practical, approach to energy efficiency. However, the concept is not just about energy. Many people invest in PH buildings because of what its occupants experience—comfort and quality of living.

BC Passive House has established a fabrication plant to build passive and high-performance buildings; there are other prefabrication companies building components to the PH standard across North America, with more expected. A recently completed project, Alta Lake Passive House in Whistler, demonstrates the level to which pre-fabrication, exemplary design, and high performance can mesh into one amazing structure.

Case study: Alta Lake Passive House
The objective of the design for this lakeside home was to create a modern, high-end interpretation of ‘green housing.’ (In addition to BC Passive House, the project team included Murdoch and Company Architecture and Planning, Mountain Resort Engineering, Dürfeld Constructors, and Arbutus Interiors). Focusing foremost on energy reduction, the clients mandated the project must embody the PH Standard with the caveat there would not be a compromise on the esthetics of the design. The use of wood was a natural choice for the design team to fulfil these requirements and meet all of the expectations for the home.

Preliminary discussions focused on typical planning and programming within the home, given some very difficult site constraints. The topography and compact nature of the site posed significant challenges. The waterfront site slopes sharply down to the east with panoramic views over the lake to the mountains across the valley. Fortunately, the desired placement of windows complemented the need to optimize passive solar gains and losses.

Windows are a significant contributor to the overall performance of a building. In the case of the Alta Lake residence, the windows were also the focal point of the design strategy to ensure the surrounding views were captured and highlighted. The residence was fitted with aluminum-clad, PH-rated wood windows.

Shading from a neighbouring home and its stand of coniferous trees interfered with solar gains on the lower levels of the south orientation. The massing of the home, therefore, was stepped and jogged on the upper floor to optimize the glazing and views without sacrificing privacy. Exterior window blinds and overhangs were used to prevent overheating in the shoulder and summer months.

Analysis of the residence using design modelling software—called the Passive House Planning Package (PHPP)—forecasts that by constructing the residence to the PH standard, the clients will save approximately 50,000 kWH/year on energy required for heating and cooling compared to an equivalent residence built to code. (PHPP is based on an MS Excel workbook that accurately describes the thermal building characteristics and performance. It can be combined with the 3D tool, designPH—a plugin for SketchUP). This represents an 80 to 90 per cent reduction in energy required for heating and cooling. The reductions are achieved through efficient design, the use of passive heating and cooling techniques; an optimized, super-insulated airtight building envelope that is fitted with high-performance windows, and a heat-recovery ventilation system.

Wood assemblies in the project
The use of wood was pivotal in enabling this project to achieve the PH efficiency requirements with an envelope system that was healthy, sustainable, comfortable, and architecturally pleasing. The envelope for the residence was constructed using a high-performance, prefabricated panel package. The main structural wall consists of standard stud 2×10 framing (406-mm [16-in.] engineered I-joist for floor and roof) sandwiched between oriented strandboard (OSB) and a wood fibre diffusion board.

OSB was used for the interior sheathing; it provided structure, shear, and both an air barrier and vapour retarder. All panel connections and penetrations to the OSB were taped and sealed with high-performance building tapes, providing a continuous, robust air barrier—this feature is critical in reaching the required airtightness thresholds. The pre-drywall blower door test achieved 0.33 ach at 50 Pa.

OSB is also classified as a Class II Vapour Retarder that works in conjunction with the exterior wood fibre diffusion board to ventilate excess vapour in the system to the exterior. In addition to reducing thermal bridging, the exterior wood fibre diffusion board provides protection from the elements while permitting drying to the exterior. A combination of blown cellulose, recycled paper products, and stone wool batts were used for insulation. An interior service wall, constructed of 2×4 lumber, provides further insulation and a cavity to run services, limiting penetrations to the air barrier. Effective R-value is 44 for the walls and 69 for the roof and floor.

The use of prefabrication further contributed to the environmental performance of the home. Through the shop drawing, ordering, and manufacturing process, the team was able to optimize the use of building materials, reducing construction waste to less than three per cent. Additionally, the prefabrication process is performed in a controlled indoor environment, increasing efficiency, quality control, and precision while reducing the occurrence of changes (e.g. swelling, mould growth, warping) in the material from exposure to weather.

Prefabrication was crucial in overcoming the challenges, increased costs, and time considerations faced due to the site conditions. Framing for the project took place offsite, in a controlled environment at the same time the foundation and site works were underway. Prefabrication offered efficiency, quality control (QC), and precision that would have been difficult to achieve with onsite construction. Once onsite, the panels were installed and the project was out of the weather within five days, dramatically reducing the onsite construction time and ensuring the materials were protected from weather damage.

The use of wood in the prefabrication enabled the design and fabrication team to be scrupulously accurate, enhancing the precision of assembly and the resulting airtightness requirements. This level of accuracy is often difficult to achieve with either onsite construction or other materials, prefabricated or site-built.

In addition to energy efficiency, the clients were focused on material choices. Through use of wood and other ecologically responsible materials, significant environmental and architectural value was achieved for a modest premium compared to conventional construction. Products were chosen for their lifecycle environmental impact, with the project team opting for materials that were sustainable, natural, and de-constructible at the end of their lifecycles.

The main building component of the facility is wood or wood byproducts. Utilizing a wood first approach for the structure of the building avoided approximately 206 metric tonnes of carbon dioxide (CO₂) emissions. (This was calculated using the web tool at cc.woodworks.org/calculator.php[4]). This does not include any operational savings of carbon emissions.

Interior design for prefabrication projects requires preplanning and an understanding of the interior volume of the space. It is difficult to adjust window heights or reposition an opening once the panels have been manufactured so previsualization tools, including the 3D models, were used in the design of the project. A collaborative approach on the window package to determine the position, opening placement, and finishes was required in the design phase to ensure correct placement to achieve the views and maintain privacy and performance goals.

Hiding mechanical corridors when roofs and floors did not have exposed floor joist cavities set up challenges that in the end created beautiful solutions. Dropped ceilings were constructed on the main floor to conceal the mini-split system. The exterior wall containing the fireplace was protruded out to accommodate a mechanical cavity, which in turn influenced the jugular angled marble block of the fireplace. The bulkheads in the family room were contained by a wood ceiling detail.

A staircase ‘tower’ was introduced early on in order to create a stack effect, allowing excess warm air to be expelled from this building. This plays an important role in maintaining a comfortable interior temperature. The feature was played up with a floating staircase and a decorative pendant installed into a complementing wood ceiling detail.

Passive buildings can be constructed with virtually any structural material. However, the use of wood fulfilled many of the owner’s and design team’s aspirations for high performance design—energy performance, comfort, quality of construction, accuracy, and low environmental footprint compared with alternative materials.

What does Passive cost?
As is the case for any design/construction project, the final cost of a PH job will vary with building size, location, design, finishes, and appliances. On high-end homes, like the Alta Lake Passive House, there was no premium for elevating the performance to passive level. On a multi-family project in Vancouver’s urban environment and a mild climate, the price may be equal or have a slight premium in the three per cent range.

During the learning phase of change, costs may also tend to be higher. After seven years of PH experience, new passive buildings built in Brussels, Belgium, fell into three equal thirds of being less expensive, more expensive, and the same cost as conventional construction.

As mentioned, Austria’s Vorarlberg province requires PH construction in all social and affordable housing. This has resulted in designers, suppliers, and builders developing the skills and the capacity to be economically competitive with conventional construction. In Canada, PH designers and builders are already becoming more efficient.

Conclusion
The Alta Lake Passive House makes it clear a project does not need to resemble the stereotypical square box with small rectangular windows in order to reap the benefits of this design methodology. Further, this case study demonstrates manufacturers in Canada and the United States are developing high-performance options for the local market—products imported from Europe are becoming less frequent.

While passive design buildings represent a very small portion of the built environment, it is destined to become a larger part of our built landscape. As we gain proficiencies in both design and manufacturing skills, ultra-high energy performance will be the rule, not the exception, because it makes sense environmentally, socially, and economically. To ensure success, an integrated, interdisciplinary design process with the consultants, contractor, and the owner will be critical.

Peter N. Moonen is the national sustainability manager for the Canadian Wood Council, and has more than 30 years of experience dealing with regulatory, environmental, sustainability, and operational issues. Moonen regularly presents on ways of achieving greater sustainability and the appropriate use of wood in Asia, Europe, and North America to design professionals, educators, and building officials. He was an organizer and session facilitator at the United Nations (UN) Timber Committee and reviewer specializing in wood and the green economy for the Forest Products Annual Market Review, published by its Economic Commission for Europe (UNECE) Forestry and Timber section. Moonen can be reached via e-mail at pmoonen@wood-works.ca[5].

Lydia Hunter provides marketing, education, and research support for BC Passive House, a Pemberton, B.C.-based prefabrication company specializing in the design and construction of high-performance panelized building systems, specialized structural panel hybrid systems, heavy timber packages, and Passive House construction. She sits on the board of the Canadian Passive House Institute West. Hunter can be reached via e-mail at lydia@bcpassivehouse.com[6].

Source URL: https://www.constructioncanada.net/active-thoughts-on-passive-design-designing-with-wood-for-next-level-green-projects/

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