Fenestration Solutions for Efficiency and Performance

New windows and doors improve building energy efficiency and occupant comfort

C.C. Sullivan

Global trends in architectural design these days seem focused on getting more transparency per square foot, throwing many of the reasons not to fenestrate out the proverbial window. This is after a few years of pulling back the reins on transparency, due to such varied concerns as energy costs, facility security, sound transmission, and glare from the sun. Yet the window-to-wall ratio, or WWR, is no longer a solitary fixation for architects and their clients. More attention today is given to enclosure U-value (also given as U-factor), the overall heat-transfer coefficient measured in BTUs per square foot of a given building assembly per degree temperature difference.

Part of the swing toward more open envelopes is end-user demand. For example, in a recent article on apartment building design by editor Penelope Green in The New York Times, a real estate broker says, “Now what most people wanted in their living rooms, they want in their bathrooms. They'll say, 'What? No view?'” Apparently it's just as fun to be seen as it is to see out, whether the spaces are sacred or profane. Newly renovated historic landmarks such as Walker Tower by the firm CetraRuddy exemplify the trend, reports Green, alongside innovative new high-rises such as 215 Chrystie Street by Herzog & De Meuron, a concrete-and-glass composition with interiors by architect John Pawson.

All this exhibitionism might come at a real cost if it weren't for a raft of new fenestration products that improve the feasibility of expanding glazed areas, whether on the roof or even on south-facing facades like Walker Tower's primary exposure. “As compared to a new roof with its R-value of about 30, a conventional skylight or window comes with an insulating value of R-1 or less,” says Mike Reeves, an executive with Wasco Skylights. “Yet, new glazing technologies such as electronically tintable glass and polycarbonate panels filled with aerogels help improve privacy, diffuse sunlight, and reduce infrared, yielding values of about R-6,” he adds. Many architects look for windows and skylights boasting a target value close to R-5 or better, which improves upon typical products bearing the U.S. Department of Energy's ENERGY STAR label.

In fact, today's building projects get a boost from window and door products like the aerogel skylights that have emerged on the scene very recently. Just as many others, however, rely on ideas that have been around for many decades. An example is the tilt-and-turn window, a hallmark of European modern architecture and a growing specification for various building types in the United States. Tilt-turns offer three separate functions in one window: a traditional casement look in the turn position, convenient top ventilation in the tilt position, and ideally a well-sealed, efficient picture window when closed. The newest versions, however, feature bulked-up profiles and thicker glazing.

New or old, these advances share a few important traits: First, they help architects meet and exceed today's challenging energy rules, including the International Energy Conservation Code (IECC) and jurisdictional “reach codes” in states from California to Massachusetts. Second, they enhance daylighting and views without unwanted interior temperature swings. Third, they add a range of performance features from improved interior acoustics and physical security to improved enclosure interfaces and enhanced durability.

“The tilt-and-turn systems stand to gain ground in today's environment of stricter energy codes, where building occupants expect comfortable interiors without the unchecked temperature swings caused by poor fenestration,” says Alan B. Wall, director of sales and marketing with Menck Windows, which recently dedicated a new manufacturing facility on the East Coast. “The German-style tilt-turn systems have robust, thick sashes and frames, which work well with high-performance gas-filled lights and even triple glazing.”

In addition to high-performance envelope projects in both the residential and commercial segments, Wall points to a few recent multifamily and institutional projects that have used these advantages to meet such voluntary standards as net-zero energy and Passive House (phius.org), which may specify quantifiable levels of both energy efficiency and occupant comfort.

With these gains in fenestration technology and performance are ideally placed to match the higher expectations of both building users and standard-setting bodies, it would seem sensible to invest time and design talent on their use. Yet even to employ today's best normative design strategies, many architects have to battle the client group's often steadfast focus on first cost, speed to market, and initial financial gain.

Architects are polishing up their skills to design better enclosures and to better convey the benefits to their clients and project teams, says Peter St. Thomas, a sales executive with 25 years of plant management and international technical expertise at REHAU North America. “There has been quite a movement on the value front in the building industry, so architects are grappling with how to find the windows that have the proper U-value,” he says.

Energy Codes Guide Fenestration

“Some architects struggle to understand how fenestration performance numbers work in terms of design,” adds REHAU’s St. Thomas. “Many don’t know how to specify new, performance-grade windows for the kind of building on the boards. Too often, they fall back on copy-and-paste specs, which may not serve their designs adequately.” He and other fenestration technical experts recommend developing a “blended specification” that identifies key performance criteria for structural performance and energy transfer, ideally with a target maximum U-value. He also sees leading architects calling out the sound-transmission class, or STC, often to help make their buildings healthier for occupants.

Projects such as schools and hospitals may have significant issues in terms of energy performance and sound transmission, says Ralph Walker, RA, LEED AP, CSI CDT, an associate with architecture and interiors firm SmithMaran. “We work with the manufacturer to develop a customized specification on acoustics, which is based on an OITC rating, or outside-inside transmission class, the most applicable designation for how much noise comes into a space through an assembly,” he says. Other key elements of the specification include thermal performance, shading coefficient requirements, and heat gain through the glass, Walker adds, as well as one final consideration: security.

Yet project designers like Walker often start the project focusing on energy performance first, because even small modifications to the glass or frame design can have an outsize impact on energy use over many years of building operations.

The key is to begin with products that help the overall assemblies meet or exceed the IECC, to ensure that energy performance is in line with regulatory and client expectations. This task has been eased for residences, as the energy conservation rules for IECC and the International Residential Code (IRC) are now aligned, as of their 2012 editions. On the commercial side, there's no more distinction between nonmetal- and metal-framed fenestration in the prescriptive provisions. But for many designers of large-scale open spaces for the public, there are recent mandates for daylighting coupled with automated shading and dimming control systems.

Starting with the basics, the 2012 IECC offers three ways to comply with the codes for residential projects and two paths for commercial construction. The prescriptive paths lay out minimum energy criteria for each product or system used for the building enclosure. For residential windows and doors, these prescriptive paths have no limitations on how much vertical glazing or how many skylights can be used on a house or apartment. However the prescriptive options are quite miserly on the commercial side: They may only be used if the total areas for glazing, windows, and skylights do not exceed the given limits. For the 2012 IECC, which is being adopted in many jurisdictions, automatic daylighting (dimming) controls are assumed for some of the more generous limits.

For example, according to Julie Ruth, P.E., a code consultant for the American Architectural Manufacturers Association (AAMA),¹ a building design can always have fenestration for up to 30 percent of its wall area. But this is relaxed to 40 percent of the above-grade wall area if daylighting controls are employed and the following two conditions are also met: At least half of the conditioned floor area receives daylighting and the glazing is specified with a ratio of visible transmittance (VT) to solar heat-gain coefficient (SHGC) that is higher than 1.1, Ruth explains. Like the three legs of a stool, however, for the higher WWR allowance to stand, all of these three design requirements must be met. A similar rule applies for skylights, allowing up to 5 percent of the roof area, an improvement on the 3 percent otherwise offered.

Changes like this one bring the IECC's prescriptive paths up to speed with leading architects and green building specialists who have advocated for the use of integrated dimming and daylighting for many years. “Why shouldn't we take advantage of the cost- and carbon-neutral resources available to us like sunlight, particularly if it can improve our health and well-being?” asks Breeze Glazer, LEED AP BD+C, a senior associate, sustainable design leader, and research knowledge manager with Perkins+Will. “One of the most effective means is to reduce daytime lighting loads by combining dimmable lighting systems with properly orientated fenestration that provides for sensible, effective natural daylighting.”

Another rule introduced in the 2012 IECC is a minimum requirement for skylight area that calls for toplighting 50 percent or more of any floor areas larger than 10,000 square feet in area, directly below the roof and with floor-to-ceiling heights of 15 feet plus. A long list of uses for the spaces makes them applicable to this minimum skylighting requirement, including convention centers and office spaces, manufacturing and warehouse facilities, retail and transportation areas, as well as any lobbies, atriums, corridors, concourses, or even storage areas.

Thermal and Structural Specs

With today's variety of glazing options, architects are specifying windows and curtain walls with a range of high-performance coatings, fills, and unit designs. “We see more projects employing specialized glass coatings, films, gas-filled and triple-glazed units,” says Menck's Wall. “Thermal bridging is carefully considered in the construction of the window assemblies, such as extruded aluminum clad on wood windows where thermal bridging can be mitigated by not adhering the cladding to the face of the window but instead suspending the aluminum to minimize thermal movement.”

For many owners seeking to improve thermal performance for existing building stock, it may not be feasible to renovate the entire envelope system. Some retrofit methods, such as adding new shading, glazing treatments, or films, may not be worth the expense and effort in certain cases, says William R. Brody, vice president with construction management firm B.R. Fries & Associates. “Instead, we see a large number of window replacement projects where the primary goal for the institutional or commercial owner is energy efficiency,” he says, pointing to recent examples by major universities and hospitals. “An energy analysis will show that fenestration is the leading source of heat loss, though it may be a close second to the roof in some cases.”

The energy-saving techniques built into replacement fenestration also benefit project teams facing aggressive state codes such as Title 24, which are “all about reducing solar heat gain by using better glazing materials,” says Wasco's Reeves. “Both Title 24 and IECC look to the National Fenestration Rating Council, or NFRC, as the guideline, and they favor total system energy efficiency that includes the framing and glazing, not merely the center-of-glazing efficiency,” he adds. For curtain wall and structural skylights, the framing is often aluminum, which is highly conductive, he adds.

Even though the skylight may be 98 percent glass and only 2 percent metal, the aluminum or steel will significantly affect its thermal performance. New framing alternatives to aluminum or wood include inner vinyl frames, which provide thermal breaks, and fiberglass pultrusions, also known as pultruded fiberglass. (A number of frame materials, including hybrid compositions, are available for punched window openings.)

While vinyl is now an option for skylight frames and skylights, some of the products are not suited to larger openings such as for structural skylights, which need hefty aluminum or other metal framing to support their weight across larger desired roof spans. “As building designs require larger and larger fenestration systems, traditional materials such as exposed aluminum and steel are typical for commercial applications,” says SmithMaran's Walker. “The key is to maintain structural integrity on the perimeter and at all corners and to provide a continuous thermal break, working with the manufacturers to identify any natural weak points in terms of structure or thermal bridging.” As an example, for continuous openings such as clerestory or ribbon windows, the lintel can become the bridge for thermal movement and moisture migration.

The NFRC independently tests, certifies, and labels the fenestration products for U-factor, SHGC, and visible transmittance (VT), which are all mandated for minimum performance. Additional ratings can be added by testing for air leakage rates—typically between 0.1 and 0.3 cubic feet per minute per square foot (cfm/ft²), where lower is better. (According to one manufacturer, the passing rate of 0.3 cfm/ft2 can be an uncomfortably drafty assembly, even as it meets the minimum standard.) For condensation resistance—given as a number between 1 and 100 where higher indicates better ability to resist condensation—architects must consider the expected conditions of each project's regional climate zone and local microclimates such as urban and coastal sites. Other factors not tested by NFRC but rated by others and essential to many project specifications include:

• Water infiltration. How much water and pressure a window system can resist to keep the water from leaking through.

• Structural performance. These ratings test for the maximum air pressure (wind load) a window can bear prior to a failure. Local codes generally establish these minimums.

• Acoustical isolation. Testing the amount of sound transmission through a window yields a rating for sound transmission class, or STC, where the higher the number, the better it is at blocking noise. (Other ratings such as OITC may be used.)

• Security capacity. These ratings measure the ability of a window to resist different types of forces, such as those caused by windborne projectiles, fire and heat, ballistics, and attempted forced entry.

For the latter category, a number of new design features mark emergency exit doors and other exterior door systems. For example, new flush panic devices for fire exits offer a break from the typical look of the bulky, obtrusive panic bars on many exit door products, while opening up egress clearances and protecting building occupants against hitting or getting caught on the bars while exiting. The smallest projection in the industry is about 1/8 inch with the door in the open position. This makes it virtually flush with the door face. When closed, it pops out to about 5/8 inches to meet all fire codes and ADA guidelines.

“The glass may be ballistically rated, but the frame should be also,” says SmithMaran's Walker, who has specified security fenestration for K-12 school projects and recommends using the federal government's ballistics rating guide as a starting point. “This requires a steel plate or similar inserted into the frame, which is then tested and rated, and only a handful of manufacturers can provide these assemblies.”

U-Factors, Heat Gain, and Light

When it comes to energy performance and sustainability, however, the IECC and other codes focus on prescriptive and performance-based paths for keeping U-factors and SHGC as low as possible while keeping VT—also given in some codes as VLT, for visible light transmittance—as high as possible. The standard NFRC 100-04 and tables given in the IECC provide allowable maximums for U-value, and the standard NFRC 200-04 and tables offer similar guidance for SHGC limits for building fenestration.

The paths for compliance with IECC include alternates to the prescriptive requirements, and many architects prefer the opportunity to design the building without prescriptive performance requirements or specific fenestration limits, for example. Two ways that IECC allow this flexibility—performance-based, whole-building design as well as the total UA alternate method—provide the design team latitude to make decisions about energy efficiency tradeoffs. The performance-based alternate path is the most flexible, however, because the UA method only allows those tradeoffs to occur within the design of the building envelope. Neither of the paths, however, affords unlimited tradeoffs—those are capped—and neither allows the architect to compensate for a less efficient envelope with a more efficient HVAC system. (Long term, many sustainability experts argue, this seems like a sensible limitation.)

Using the residential IECC 2012 edition as an example, SHGC is capped in the Southern climate zones at 0.50, but there is no U-factor cap in these warmer areas. Yet there is a U-factor cap for cold northern regions, given as climate zones 6, 7 and 8. In between, in areas such as Missouri and Utah, project designs may not exceed the U-factor of 0.48. If the design team is using an alternative path for compliance with IECC, limits on U-factor and SHGC may be given for skylights, windows and exterior glazed doors. Bounded by prescribed caps, architects can make any tradeoffs in efficiency that they feel benefit the project's requirements for budget, schedule, aesthetics, and performance.

For the special case of exterior doors with glazing, if the framed assemblies total less than half glass in measured area, they are considered opaque doors; more than half glass, they are glass doors that are subject to specific limits similar to windows and skylights. All doors are considered fenestration in the IECC's view, however, and even opaque doors must be factored into building energy calculations. As an example, the U-factor of an opaque door in the IECC's 2012 version may not exceed 0.35, says AAMA's Ruth, with an exception made for a single opaque door of up to 24 feet in total area, which may be exempted.

The benefits of meeting the requirements of the IECC go beyond mere code compliance. They also include a fundamental technique for reducing facility operating costs and carbon footprint.

A recent analysis reported by Menck shows the bottom-line results of using better fenestration technology. Under assumed conditions, a single-pane window annually requires 1.65 gallons of heating oil per square foot to maintain interior temperatures, where a double-pane uncoated window will reduce that need for heating oil by 49 percent to 0.81 gallons per square foot of window area. To reduce that by another 42 percent, specify a double-pane insulated glass and only 0.34 gallons of heating oil are needed annually, according to Menck's analysis. A triple-pane insulated glass further reduces the energy need by 56 percent, to 0.19 gallons of oil per year to maintain heated interiors.²

Window Wall Interface

Critical to the energy-efficient design of a building envelope with fenestration is the detailing of the window-wall interface, an area of significant research and development in recent years. Far from simple joints, these interfaces are locations of multiple system details and a high degree of coordination between various trades, says B.R. Fries' Brody. Leading energy-efficiency advocates and enclosure consultants like Wagdy Anis, FAIA, a principal with Wiss Janney Elstner, Inc., have described, for example, how air-barrier continuity must be rigorously maintained at window openings. The architect's documentation must protect against improper design and installation techniques can lead to pathways for air leakage that drastically reduce building efficiency, say the experts.

One benefit of European tilt-turn technology, says Menck's Wall, is that the product types have been specifically designed to enhance their effective installation at the window-wall interface. These and other window products are designed with high-performance fastening, flashing, and insulation continuously and securely assembled around the window-wall interface.

“It's important for us as the manufacturer to involve the architect and builder early in the process and create the details for the window to fit properly and securely into the wall,” says Wall. “We encourage the architect to submit their wall section CAD files,” he adds, so they can drop a window design into the section and show how all accessories work together. These should include uninterrupted air and moisture barriers indicated and with continuous insulation to address sound and efficiency needs as required by the design intent.

Many of the European window and door products, such as the tilt-turn systems used increasingly in the United States, are made with sturdy frames of metal or unplasticized polyvinyl chloride (uPVC), a rigid and durable material that contains no pthalates or bisphenol A (BPA), unlike its cousin PVC. The growth of interest in uPVC material reflects its effectiveness in various building uses. As window and door framing, uPVC does not deflect or flex much as compared to other, and it resists fire, weather, oxidation, sunlight and ultraviolet rays, mold, and most common chemicals. It is also recyclable, according to manufacturer sources, and provides a good thermal break as compared to metals.

The material uPVC is often marketed as “rigid PVC” or unplasticized poly, and it is also simply called “vinyl” in the context of vinyl siding and other commonly used materials in the United States. It is also used extensively as plumbing and drainage piping. For architectural applications, uPVC provides an effective substitute for painted wood, and uPVC can be made in a range of integral colors and patterns, including a wood-look finish. The material also benefits window frame sections by helping reduce thermal bridging and overall sound transmission as compared to metals.

A Sound Experience

Overall, there is growing interest in better sound attenuation as fenestration systems become more effective in controlling thermal performance over large areas. In general, while sound transmission includes both airborne and structure-borne vibration, the STC single-number rating describes only the window assembly's designed ability to resist airborne sound transfer within the frequency range of 125-4000 Hz. STC can be improved by adding air space, mass or isolating materials within the window assembly.

“Today, leading manufacturers are guiding architects to specify STC in their projects,” says REHAU's St. Thomas. “With the typical goal-setting for better STC in the industry, for many window and door products you really need to bump up the glass structure to hit the desired numbers. However there are European window technologies that generally offer a higher baseline STC.” The typical windows in Europe, where uPVC tilt-turn products are commonplace, have such sound-abatement features as compression seals and multipoint locking, St. Thomas adds.

Recent U.S. projects built using these window designs include The Montage in Reno, Nevada, one of the largest adaptive-reuse projects in the sector. The architecture firm Antunovich Associates reimagined the 23-story former Golden Phoenix Hotel and Casino as a mixed-use residential community with 380 living units including loft, penthouse, and pool terrace residences. In the conversion design, one highly marketable feature—floor-to-ceiling windows, incorporated to maximize daylighting—was initially specified as commercial-grade, aluminum-frame systems. Yet the architects and project team saw the benefits of installing uPVC tilt-turn windows and top-of-the-line uPVC doors for energy-saving performance and noteworthy aesthetic appeal.

Like other large adaptive-reuse projects, The Montage offers a number of performance benefits to both occupants and the property owners. Sustainable design aims of the Antunovich Associates team included a substantial long-term reduction in environmental impact and carbon footprint, which the fenestration products would reinforce. In terms of the lifestyle experience for residents, the windows help reduce hot spots and cold spots and they reduce noise infiltration when closed. For opening, the windows can be used either by tilting to create a hopper-type or awning-type opening, which often maximizes effective natural ventilation. In their turn position, the windows basically operate as convenient casement units for Reno's high-altitude, low-rainfall yet low-evapotranspiration climate.

In other climates and settings, improvements to curtain wall, window wall, and storefront systems are opening impressive vistas while also controlling thermal and sound variables. Examples include urban cultural and academic settings as well as transportation hubs, where both noise control and visual transparency are key project aims.

In an example that merges both project types, the architecture firm Architype created an airport visitor center in the natural hilltop landscape of Chiltern Hills at Dunstable Downs in the southeast of England. Commissioned by the local county council and The National Trust, the project was envisaged as a destination for all visitors, not just those arriving or departing by plane. Architype responded with a purpose-designed facility marked by large expanses of curtain wall and an expressive pitched roof that would meet high standards of sustainability. “The development of the center has been designed with a rigorous environmental agenda, with great consideration given to reduction in use of fossil fuel energy and the adoption of a palette of ecologically sound and nontoxic materials,” the firm said in a project statement.

For the fenestration system, Architype detailed a post-and-rail façade construction with special shapes employing triple glazing with a special tint and coatings. Filigree views of the profiles help form a “harmonious overall appearance” for the modern building, according to the glass façade maker. For visitors, the heavy façade system provides a relatively consistent perimeter temperature for comfort as well as broad views of the hilly green countryside. The architects incorporated a range of green technologies to supplement their effective enclosure design, including a wood chip boiler, rain water recycling, and a novel windcatcher channel that draws air from outdoors into the building through a 295-foot-long underground concrete “earth duct,” according to Architype.

Climate Responsive, Super Insulating

The use of wood, rain, and wind helps give buildings like the Chiltern airport facility a very small carbon footprint, while the glass expanses improve the potential benefits of the sun: chiefly passive solar heating and illumination.

Yet novel fenestration designs also benefit from relatively novel building materials, such as Space Age products like aerogels. While the materials are hardly brand-new, they have been proven to work and have a good track record extending back a decade or more. In fact, the scientist Samuel S. Kistler of Stanford University and the College of the Pacific, Stockton, California, reported on novel laboratory aerogels and “jellies” in the journal Nature back in early 1931. Kistler and collaborators “prepared silica, alumina, nickel tartarate, stannic oxide, tungstic oxide, gelatine, agar, nitrocellulose, cellulose, and egg albumin aerogels,” and remarked that, “the new physical properties developed in the materials are of unusual interest.”

One property that proved Kistler's prescience is their very low density, with aerogels comprising as much as 95 to 99 percent air or other gases, giving them the lowest densities ever recorded for any materials, let alone building insulation. They also admit plenty of light, thanks to their relatively high VT values. Utilizing a nanotechnology solution, some of the aerogels applied to window and skylight systems provide a valuable, highly effective thermal insulator that is also environmentally sound, according to Wasco's Reeves. “On a nanoscale, these aerogels permanently stop connective, conductive thermal transfer without an appreciable drop in light transmission,” he explains, yielding good thermal performance and glare-free, full-spectrum diffused light.

A skylight assembly with an aerogel was used for the nation's first LEED Platinum grocery store. Architect Rick Ames, AIA, LEED AP, of Boston's Next Phase Studios worked with the green building consultant Gunnar Hubbard, AIA, president of Fore Solutions, and daylighting consultant Clanton & Associates to develop a design using more than 50 thermal skylights for both general and task lighting and to achieve optimal daylighting conditions in critical areas of the store. The double-paned, polycarbonate glazed skylights are insulated with a layer of lightweight, translucent aerogel. The aerogel-enhanced fenestration provides good insulating values and SHGC values, adding up to openings that are about six times as energy efficient as conventional skylights. Shoppers below enjoy diffused, glare-free full-spectrum daylight, which studies show can have a positive effect on worker productivity and can even boost sales.

This introduction of good-quality daylight is increasingly important to design teams, says the architect Walker. “Some products, such as self-tinting windows, can create a natural color shift that affects the interiors of buildings,” he explains. “So you need to select finishes, fabrics, and coatings for the interior with that expected color shift in mind.”

Another key consideration for window and door selection is structural and impact resistance, says B.R. Fries' Brody. “For skylights and sloped glazing, you need to consider all the loads that can cause positive or negative design pressures, including wind, snow, and dead loads,” he says. “When designing vertical systems, one of the main issues is whether the project is in a high-wind area or subject to special codes for severe weather.” According to AAMA, the building's exposure category and design wind speed dictates the needs for special inspections, such as the Exposure Category D, which calls for special inspections of buildings near oceans or large lakes where design wind speeds are at least 110 miles per hour.

“ANSI and UL tests for window assemblies vary dramatically depending on the climate and jurisdiction,” says the architect Walker. “There are places where we naturally expect very strict requirements, such as in Miami and Oklahoma. So it's both a global and a local issue.”

Active Design and Passive Thinking

Window selection is often driven by occupancy mix and activities as much as energy efficiency goals or comfort needs, adds Walker. For example, the architecture firm SmithMaran recommends allowing for operable windows to increase natural ventilation, but building-wide control of ventilation and related HVAC operations must be considered. “Also, there are window types that allow for ventilation at the top or the bottom, which is advantageous in certain kinds of spaces,” he adds. “But occasionally you create a ventilation short circuit, where fresh outdoor air comes in at the bottom and just rises and escapes above.”

When it comes to egress, there are similar complexities depending on the occupant mix. For example, in many commercial spaces the window systems double as means of egress. In these cases, the architect may work with the owner improve the fenestration design for fire safety and other life-safety reasons, especially in hospitals, universities and similar facility types. On the other hand, elementary schools and multifamily buildings may need to limit the opening of windows to protect children, so those can't serve double-duty as egress.

In these cases, active facility management and occupant education can be helpful, as well as selection of a suitable window type.

Exemplifying the twin challenges of occupant preferences and energy efficiency is the Passive House standard. This is a set of design principles used to “attain a quantifiable and rigorous level of energy efficiency within a specific quantifiable comfort level,” according to Passive House Institute U.S. (PHIUS), which promulgates the approach. The underlying directives are essentially six building-science principles that apply to both residential and commercial projects:

• continuous insulation through the envelope without thermal bridging;

• a very airtight enclosure to limit air infiltration or loss;

• the use of high-performance doors and windows, such as triple glazing;

• balanced heat- and moisture-recovery ventilation and minimal space conditioning;

• and managed solar gain for controlled heating and minimized cooling needs.

Door and window makers have risen to the challenge, in part motivated by the focus on fenestration components. For example, a project called Bernhardt Passive House on Vancouver Island, British Columbia, Canada, employs large, energy-efficient doors and windows. Designed by Greg Damant of Cascadia Architects in Victoria, the project comprises a two-family residence for a young family of four, with active grandparents in a suite, according to Bernhardt Contracting.

“Windows exposed to winter sun provide most of the heating for the home, but cannot provide the thermal performance of a wall,” according to Bernhardt Contracting. “Glazing is therefore planned to maximize solar heat gain in the winter through south-facing windows that are shaded in warmer months, and minimize north-facing windows. East and west-facing windows require shading from morning and afternoon sun in warmer months. Where windows are not shaded by deciduous trees, roof overhangs or trellises are planned.”

The contractor adds that they “have chosen to install great windows,” focusing on thermal comfort and long-term air tightness for greater design flexibility and larger window areas. Using a number of European-style tilt and turn windows and doors, with a certified fiberglass/uPVC frame having a U value of 0.79 and triple-glazing with edge spacers designed to giving a glazing U value of 0.73.

“Windows and doors are some of the most critical components of Passive House construction,” the contractor's website confirms.

C.C. Sullivan is a marketing communications consultant specializing in architecture and construction.