Introducing the Passive House system: A new standard for building green

by Katie Daniel | October 27, 2015 12:05 pm

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by Gita Nandan, RA, LEED AP
The architectural community is at a tipping point. Specifiers and their design teams are moving closer to super-energy-efficient performance across a spectrum of building types and portfolios, including the ‘deep energy retrofits’ of recent years. This is good news—U.S. commercial buildings account for 72 percent of domestic electricity use and 36 percent of natural gas consumption, according to a 2008 report[2] by the U.S. Department of Energy (DOE), and they contribute an eye-popping nine percent of global greenhouse gas (GHG) emissions. A solution many architects and owners are turning to is Passive House, a relatively new standard focused on airtightness, high thermal values, energy-attuned material selection, and the use of natural ventilation and lighting.

Applying Passive House makes possible reductions in energy consumption as much as 90 percent, while still maintaining beautiful design and cost-effective construction. Extrapolated across every building in America, that means a potential reduction of at least 2.25 billion tons of carbon dioxide (CO₂). Such lofty numbers aside, Passive House is coming into the mainstream as a standard that aids the building industry to minimize energy consumption and meet larger global goals.

Passive House has its roots in Europe, where in 1988 the Swedish professor Bo Adamson and German physicist Dr. Wolfgang Fiest, also later the founder of the Passive House Institute in Germany, originally developed the Passivhaus standard. After several decades, this movement has finally taken off, spreading from Central Europe to the United States and across the globe. Today, an estimated 50,000 structures have been built to these standards around the world, of which approximately 10,000 are certified—it is clearly a mainstream building path.

While many professionals associate certified Passive House buildings with the single-family residential market, over half are commercial buildings. These run the gamut from schools and natatoriums to multifamily complexes and office buildings, all created by project teams seeking to lower energy costs and consumption while providing durable, comfortable buildings suitable for the 21^st century.

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The Passive House standard achieves these ends through a set of mandatory performance goals targeted at the building envelope. It is overseen by the Passive House Institute (PHI), the international organization with local chapters and certifiers in each country. In the United States, Passive House Institute US (PHIUS) also provides certification.

PHIUS severed ties with the international organization in 2011, primarily over concerns related to climate-related design and the influence climate has on the standard: PHI believes the standard can be applied globally with local knowledge and customized detailing, whereas PHIUS believes the standards must be flexible and adjusted to regional needs.

The standard put out by PHI has a global application, and it is the designer’s job to customize the building envelope in relation to climate to achieve the standard’s performance criteria. PHIUS[4], on the other hand, has developed PHIUS+ 2015: Passive Building Standard−North America, supported through a DOE[5] grant that acknowledges a variety of climate zones across the United States. This standard modifies the required targets through a formula and includes cost-optimized performance options; metrics are provided for more than 1000 locations on the PHIUS guidance map, found on the organization’s website.

Overview of the standards
This article refers to “Passive House” standards, but the references are more specifically those in the PHI program. Again, the major difference between that standard and the PHIUS one is the latter has localized goals, while the former is a single goal for all projects worldwide.

Either way, Passive House strictly looks at energy performance in parallel to thermal comfort. It is not a holistic green building approach such as the U.S. Green Building Council’s (USGBC’s) Leadership in Energy and Environmental Design (LEED) or the Building Research Establishment Environmental Assessment Methodology (BREEAM) programs found in the United Kingdom, which include standards related to water, transportation, materials, and other aspects. (In some cases, Passive House Certification is currently being adopted and accepted into these wider-reaching, third-party green building programs.) There are different paths for certification based on new construction versus renovation, each with their own set of target goals, but overall all certifications address the same categories for achieving energy efficiency.

The PH standard sets firm maximum targets in three categories:

• total heating and cooling demand per area;
• total energy demand (including lighting and appliances) per area; and
• total air leakage.

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Space heating energy demand
Space heating energy demand cannot exceed 15 kWh/m² (4.75 kBtu/sf) of net living space
(i.e. treated floor area) per year or 10 W/m² (3.17 Btu/sf) per hour of peak heating demand. In climates where active (mechanical) cooling is needed, the space cooling energy demand requirement roughly matches this, with a slight additional allowance for dehumidification.

Primary energy demand
The total energy to be used for all domestic applications (i.e. heating, hot water and domestic electricity) must not exceed 120 kWh/m² (38 kBtu/sf) of treated floor area per year.

Airtightness
In terms of airtightness, a maximum of 0.6 air changes per hour at 50-Pa pressure (ACH50) must be verified by an onsite pressure test, with results given in both pressurized and depressurized states.

Thermal comfort
Thermal comfort [7]must be met for all living areas during both winter and summer, with not more than 10 percent of the hours in a given year over 25 C (77 F).

Five basic principles
Passive House does not provide prescriptive details on how to achieve the Passive House standards outlined above, as it is a performance-based set of goals. Designers are encouraged to customize building envelope details to their climate, building typology, and construction needs, allowing for innovative building techniques.

There are five basic Passive House principles at the core of achieving the properly designed envelope to earn Passive House certification:

• a thermal bridge-free design;
• superior windows (which can be Passive House-certified products);
• ventilation with heat recovery;
• high-quality insulation; and
• airtight construction.

These five principles guide the architect and engineer design process throughout, beginning from concept to construction, to ensure the project meets Passive House goals.

FURTHER RESOURCES

For more reading online regarding Passive House and its underlying concepts, visit the following: www.passipedia.org (international Passive House conferences); www.phius.org (Passive House Institute United Sates); www.phius.org/alliance/home (Passive House Alliance); www.aphnetwork.org (North American Passive House Network); www.passivehouse-international.org/ (International Passive House Association); and www.greenbuildingadvisor.com/blogs/dept/musings/hrv-or-erv#ixzz3jepqPBcX (text references).

Thermal bridge-free design
Eliminating thermal bridges prevents heat from flowing through a building envelope. Heat follows the easiest path from warm to cold surfaces. When not detailed correctly, construction materials such as metal studs, steel headers, and metal fasteners can cause severe thermal bridging and increase energy usage due to heat loss. Various construction alternatives using such techniques as insulating porous concrete masonry units (CMUs) and insulation stops can help minimize thermal bridging.

An important tool for the design and engineering team to identify the existing conditions of thermal bridging is the infrared (IR) camera—a device that produces visualizations by detecting heat as IR energy and then converting it into electronic signals processed to produce thermal images. The images allow designers to read where heat loss is occurring in the building envelope, often revealing surprising conditions invisible to the naked eye.

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Superior windows
Window selection is critical in any building envelope, but Passive House brings a higher factor of importance due to their typically lower relative energy performance and their often large overall surface area. Passive House-certified windows have been developed over the past decade to help eliminate this envelope Achilles’ heel.

The Passive House recommended standard is </ 0.8 W/m²/K (</ 0.14 Btu/hr-sf-F) equivalent to an R-7. To achieve this performance, windows are constructed with nonconductive frame materials such as wood or fiberglass and with triple-pane, gas-filled lites. The U.S. marketplace is limited in such offerings (though a recent check shows a few domestic companies with offerings), but items like Passive House windows may be specified through European manufacturers.

The Passive House window standard is not a requirement, and if lower R-values are specified the energy efficiency levels must be compensated for in the envelope insulation. The typical U.S. window meeting building code varies per climate from less than 1 R-value (U-value of 1.2) in Climate Zone 1 to 2.8 R-value (U-value of 0.35) in Climate Zone 8, according to the 2009 version of the International Energy Conservation Code (IECC). Passive House standards range from 2.5 to 7.0 times more stringent.

Insulation
Deep insulated wall assemblies make up the core of the envelope. For Passive House, most buildings require envelope performance levels in the range of R-40 to R-60 for walls, R-50 to R-90 for roof systems, and typically about R-30 to R-50 for sub-slab assemblies. Such insulation levels may be about four times the levels required by local building code, and may yield a much deeper, thicker wall design. Rather than using stud-wall cavity-based insulation systems, alternatives such as insulated concrete forms (ICFs), exterior insulation and finish systems (EIFS), and various other continuous insulation (CI) wall details allow for a thinner wall section while achieving necessarily high insulation values.

Airtight construction
The standard’s airtightness requirements are among the most challenging requirements for U.S. design teams trying to achieve Passive House criteria. Success relies heavily on the general contractor’s expertise and attention to detail, ensuring all openings and penetrations large and small are flashed and sealed before the envelope’s closing. There are several effective materials in the marketplace for these details, including a variety of window tapes, caulks for joints and seams, and airtight electrical outlet boxes. This process visually differentiates Passive House projects during the construction phase, when observers can see the wrapping and taping of substrates, windows, and penetrations.

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The airtightness measure of 0.6 ACH50 required for achieving certification is verified onsite by means of a blower door test. (PHI has created an energy retrofit standard, EnerPHit, which requires a more achievable 1.0 ACH50 for certification.) For Passive House, a European standard—EN 13829, Thermal Performance of Buildings: Determination of Air Permeability of Buildings−Fan Pressurization Method—is often referenced. While it is similar to ASTM E779, Standard Test Method for Determining Air Leakage Rate by Fan Pressurization, there are slight differences in the timing of the tests, how volume is calculated, and methods for final reporting. Conducting a blower door test early in the construction phase helps indicate any remedial steps needed, envelope areas requiring added air sealing, and what should be next in the path to Passive House certification. A final test is conducted when the envelope and mechanical systems are completed.

Ventilation
‘Passive’ House is perhaps a misnomer—ventilation in this case is not a passive design feature (see “At a Standard’s Core, Passive Design Precepts,” below), but instead requires an active mechanical system to move stale indoor air out. No longer is incidental infiltration an acceptable alternative for ensuring the fresh outdoor air supply. Careful design of the ventilation system by the engineering team is important to ensure fresh air is introduced in all occupied rooms. Typical ventilation systems specified are energy recovery ventilation (ERV) or heat recovery ventilation (HRV) units; depending on the size of the building and the spatial configuration, a project may require multiple units.

HRV systems allow heat from the warmer air stream—stale air in winter, fresh air in summer—to be transferred to the cooler air stream. In the winter season, the HRV ‘recovers’ a portion of the heat that would have otherwise been exhausted and lost to the exterior. This heat transfer occurs without any mixing of the two air streams.

An ERV does everything an HRV does and allows some of the moisture in the more humid air stream—usually the stale air in winter and the fresh air in summer—to be transferred to the drier air stream. Ventilation is typically exhausted from bathrooms and kitchens, whereas it is supplied to the living room and bedrooms. These ventilation systems should run at about 90 percent efficiency, and help heat and cool the building in the shoulder months. This eliminates the need for other individual ventilation systems and, in this way, minimizes any additional penetrations through the envelope that could cause heat loss. If ducts are associated with the ventilation installation, the runs should be minimized, kept as straight as possible, and built without flexible ductwork, which can kink.

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Getting certified
How do buildings get certified? An important part of the standard is the Passive House Planning Package (PHPP), which includes an energy-modeling tool so the design team can analyze building components and specific design elements to study how various options affect energy performance. For example, one could change the amount or type of insulation or the size and location of windows, and output data on how those changes affect the building’s overall efficiency.

Since PHPP comes early in the certification process, the design team and owners can often determine from the project’s outset—even before concept and site selection, in some cases—some key design and specification criteria. Ultimately, a set of documentation is required to prove the standards are met, and checklists are provided through the organization’s websites.

It is highly recommended to involve a Passive House-certified consultant with the design team and overall process to ensure every detail is considered to meet the guidelines. Increasingly, architectural practices are training staff members to the standards. The Passive House Institute and PHI-US each offer varied educational opportunities from a one-day introductory lecture to a professional, 10-day Passive House Designer course.

The Passive House standard is typically geared to new construction. With so many retrofit projects undertaken today to meet Passive House, though, the parallel standard EnerPHit was launched in 2012. EnerPHit acknowledges existing buildings are more challenging in terms of achieving energy efficiency goals. Existing conditions may require costly installation methods to achieve levels similar to those for new construction.

Another issue is the orientation of existing buildings that respond to criteria other than maximizing useful solar gain. In northern climates, without solar access to act as the primary heating system, the amount and cost of insulation required can be prohibitive. With these issues in mind, EnerPHit’s certification rules are less stringent than those for Passive House—but still quite rigorous. Studies listed on the online resource Passipedia show EnerPHit[11] projects yield about 85 percent greater efficiency levels than typical retrofits.

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Highlights of EnerPHit standards include:

• less than 25 kWh/(m²) (about 7.9 kBtu/sf) for annual heating and cooling;
• airtightness better than 1 ACH50; and
• total annual energy usage £ 120 kWh/m²
  (38.1 kBtu/sf).

With Passive House, it is the fabric first and relies on the building alone to achieve the standard. However, net-zero buildings and net-positive buildings have gained momentum, especially with the launch and success of the Living Building Challenge. While the term has several definitions, a net-zero building is generally understood to offset its electrical consumption with an alternative energy source on site. A net-positive building is one that produces more power than it consumes and shares that resource with the local utility grid or adjacent buildings.

PHI’s founder Fiest has taken notice, and recently launched two additional Passive House certifications[13] to address this: Passive House Plus for net-zero buildings, and Passive House Premium for net-positive buildings[14].

Conclusion
Developers and building owners often ask the design team, “What is the return on investment for construction to Passive House?” This is a good question considering the reputation[15] green building holds as an incremental or additional expense to construction overhead. In Europe, these standards have been in practice for so many decades buildings tend to be delivered at the same cost as standard construction. In the United States, there is a wide range of options and opinions, so local attitudes and labor rates may affect the budget. In urban areas, five to 15 percent is the driving standard for greater energy efficiency, and does not account for the real payback to the owner, which depending on utility rates can be as fast as 18 months.

Additionally, there are multiple co-benefits that are difficult to quantify, such as improved comfort, better indoor air-quality (IAQ) controls, and more durable buildings with greater resale value and market longevity. Passive House projects also tend to provide for excellent resiliency and thermal comfort in emergency situations, such as power outages.

While the design community searches for solutions on how to meet the ever-increasing energy efficiency demands, Passive House is proving to be a leading path for designers and specifiers. The standard is becoming a nationally accepted tool beyond single-family dwellings, and growing in the commercial and multifamily sectors. As future energy costs rise, developers and building owners will demand more cost-effective solutions. One should expect Passive House buildings to stand among your neighbors in future developments; while certification is a lofty goal, it can only be beneficial in our climate-changing world.

AT A STANDARD’S CORE, PASSIVE DESIGN PRECEPTS

[16] by Jorge Mastropietro, AIA Before taking on Passive House as a certification path, it helps to consider the fundamental and underlying principles that make it work so well. These concepts inform many of our longstanding construction practices that have been proven to work—and should be part of any modern building design. This author’s childhood home was in Buenos Aires, Argentina, where the summers were naturally hot and sweltering—an average January temperature of 25 C (76 F) and dewpoint averaging 21 C (69 F). When the temperatures descend in winter months, it is mild (12 C [53 F] average) and humid air still endures. Our traditional, vernacular home in the center of the city dated from the 1800s—a type known as a casa chorizo. Like its sausage namesake, the rooms are linked one after another alongside a courtyard. Reflecting back, what I remember most—in addition to the fresh fragrance of jasmine and azaleas in the luminous courtyard—was always feeling comfortable indoors. With cross-ventilation, the house stayed pleasantly cool, even though we didn’t have air conditioning or ceiling fans. Things changed when I moved out and took my own apartment in a brand-new multifamily building with sweeping views across the metropolis. The sun blasted into large windows, and the space became unbearable in the summer. Installing blinds over the windows and a through-wall HVAC unit, which ran 24 hours a day, solved this problem. However, it raised another: The beautiful city views were shrouded in white fabric, and gone were those memorable summer breezes. [17] It set in stark relief the advantages of the casa chorizo style: its thick masonry walls provide exceptional insulation and airtightness; open transom windows let convective currents move warm air above doors and windows—and out of the building; its veranda buffers against the high summer sun, while allowing lower-angle winter sun to project light into the bedrooms; and grape vines growing above offer handsome, seasonal shading. In fact, these are some of the basic passive design strategies that underlie the superior performance expected for the Passive House standards such as Passive House Institute US (PHIUS). Efficiency comes from a measured response to local climate and site conditions to maximize occupant comfort. The same design approaches cut the need for mechanical heating and cooling. Passive design approaches can reduce temperature fluctuations, improve indoor air quality (IAQ), and make a home more enjoyable to live in. As PHIUS notes, architects can implement passive building by incorporating a well-defined “set of design principles used to attain a quantifiable and rigorous level of energy efficiency within a specific quantifiable comfort level.” The group offers five building-science tenets for application to any building type, including: continuous insulation (ci); an airtight building envelope; high-performance windows and doors; balanced ventilation; and managed solar gain. As it turns out, my childhood’s casa chorizo was embedded with ancient intelligence. As is codified in today’s Passive House certifications, its builders know how to design for both comfort and resource efficiency—using a venerable, passive approach.

Gita Nandan, RA, LEED AP, is an architect, designer, educator, and community resiliency leader. In 2000, she cofounded the award-winning design firm thread collective LLC, where she is principal. Working in the field for more than 15 years, Nandan has overseen design and construction on a wide range of project types from single-family homes and mixed-use buildings to flood-protection plans and working farms on public housing property. She has been involved in sustainable design policy and code creation groups, serving as a member of the Homes Committee for Urban Green Codes Task Force and the Building Resiliency Task Force, both in New York City. Nandan received her master’s degree in architecture from UC Berkeley and is a registered architect in New York and New Jersey. She can be reached at gita@threadcollective.com[18].

Source URL: https://www.constructionspecifier.com/introducing-the-passive-house-system-a-new-standard-for-building-green/

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