Designing and constructing a net-zero-energy building requires an envelope that provides effective insulation and controls solar gain. An associated goal is that the envelope contributes to the interior environmental quality enjoyed by the occupants. Technologies in use over several decades have added another goal that informed observers advocate integrating into the design process: making a positive contribution to a building’s energy balance via integration of active technology into the facade. Though not yet adopted into mainstream use in the U.S., their promising use overseas and the potential researchers are uncovering could bring about constructive changes.

Photo courtesy of Onyx Solar Group

The spandrel glass of Milan’s Gioia 22, an office tower by Pelli Clarke and Partners, includes approximately 55,000 square feet of monocrystalline silicon photovoltaic cells.

Because buildings account for 40 percent of global energy consumption, informed and responsible architects, engineers, and owners recognize that every measure that can enhance their energy performance is worth considering. An adaptive facade not only can aid in controlling solar energy input but in some cases can transform sunlight and rainwater from adversarial elements to useful resources. In a three-tier approach to energy efficiency (load reduction, passive systems such as shading, and active energy-harvesting systems), adaptive facades can address at least the second and third of these strategies (Lechner 2008), and in certain cases all three. Generating at least some of a building’s power locally, rather than relying on transmission lines, also carries the promise of mitigating the power-grid inefficiencies that hinder decarbonization efforts on every scale.

An envelope that not only conserves energy but harvests it can function as an active organ within the building-organism, as the leaves or petals of plants or the skin of humans and other animals process sunlight in their different ways. This biological metaphor, viewing a building as an organic system and its facade as resembling a living skin, membrane, or botanical component more than an inert shell, can in some cases literalize the metaphor: increasing numbers of advanced buildings have incorporated living materials into their facades, not only emulating nature’s energy-transferring processes but marshaling them directly in the form of green facades or “biofacades” (Bonham and Kim 2022; Patterson 2022).

Net zero remains an asymptotically approachable ideal for some buildings while becoming an increasingly realistic goal for others (with the customary caveats about calculations, questionable offsets, and greenwashing). To date, most adaptive facade systems help reduce a building’s energy burden and carbon footprint incrementally toward net zero, though certain proof-of-concept projects demonstrate that crossing the zero line and reaching net-positive energy balance is possible, at least under research conditions. There is no building category that cannot benefit from analysis and upgrade of its facade's energy management: retrofitting an existing building with an active envelope reduces the waste of embodied energy and carbon involved in demolition, while designing a new building with its energy profile included in the planning from the early stages ensures that the facade and other components add up to a purposefully integrated system.

The relevant terms and philosophies proliferate (active facades, adaptive facades, smart facades, green facades, net zero, Passive House/Passivhaus, Aktivhaus, and others), yet the common goal is clear: to improve on the practices that have made too much of the American built environment a profligate user of resources, an intensifier of the urban heat-island effect, and a contributor to buildings’ share of global energy consumption.

Some specialists in advanced facades recommend that the design, engineering, and construction fields rethink assumptions that are long overdue for drastic change. Professionals working in the transition area between research and day-to-day practice advocate fundamental reconception, not maintenance of a steady state, given the growth in world populations, the proportion of urban residents, and the demands for new housing, transportation, and infrastructure. “Sustainability is no longer an option,” says Enrica Oliva, COO and partner of Werner Sobek New York (WSNY), a pioneering firm at the intersection of engineering and design. “We can no longer afford to just build the way that we used to—to just build the way that we know because it’s faster or because they may be perceived as cheaper, because resources are running out.”

Oliva emphasizes a specific definition of the challenge: it involves reduced reliance on fossil-fuel-based energy systems, not energy use generally, and it requires a close degree of collaboration between architects and engineers. “We’re not running out of energy,” she says. “We’re running out of resources. The sun is still there. It’ll be there for a very long time. So if we use the right sources of energy, we will not run out of that, but the problem is, we’re using resources that are getting depleted, and that very soon will put us in a position where we can no longer afford to live here.” Her firm’s work on lightweight and adaptive structures is guided by a concept that its founder Sobek defines as “Triple Zero” (buildings with zero emissions, zero energy, and zero waste generated), with the goal of moving beyond Passivhaus efficiency standards so that a building becomes an energy-producing Aktivhaus.

Methods of decreasing a building's dependence on the external power grid through local energy harvesting include a technology that has become broadly familiar, rooftop-mounted photovoltaic (PV) cells. The amount of available roof area limits their contribution, however, particularly in urban settings; some buildings manage to gather low-hanging fruit by extending PVs to the larger surface area of the exterior envelope. Along with conventional glass curtain walls reaping thermal energy and offering increasing control of daylight, advanced glazing systems are available using dynamic solar shading and photochromic, electrochromic, or thermochromic glass. Building-integrated photovoltaics (BIPV) have been explored and promoted, more extensively overseas than within the United States, though opinions differ over whether this approach can be scaled up economically to fulfill the promise its early advocates have envisioned. Additional mechanisms to consider include supplemental hydronic heating, rainwater collection, and biophilic air treatment.

Photo courtesy of View Glass; rendering by Neoscape

The retrofit project at 111 Wall Street, a 25-story Class A office tower in New York’s Financial District redesigned by STUDIOS Architecture, reclads the building with electrochromic glass, which controls thermal input and energy consumption along with allowing high-definition transparent displays.

The U.S. lags behind Europe in applying advanced facade technologies in the field, commentators observe. This discrepancy reflects a convergence of factors, including the higher cost of energy in Europe, which increases economic incentives for thermal performance; the cost of American certification programs (e.g., Underwriters Laboratories or FM Approvals) for European firms that have developed advanced technologies but have not gained a foothold in the American market; the relative unfamiliarity of U.S. tradespeople with the newer systems; and the generally more rigorous codes abroad, except for certain bellwether cities or states where environmental concerns are expressed in codes like New York City’s Local Law 97 and California’s Title 24.

Leading American architects and engineers are well aware of the higher standards and openness to innovation that are more prevalent in different regulatory and business environments. The urgency of the need to accelerate the transition to renewable forms of energy is no mystery to any informed observer of the American built environment, though the structure of economic incentives, some observe, has been a barrier to conversion to better-performing envelope technologies, not only on the cutting edge of research but in areas that are relatively well known.

“There are other strategies for energy harvesting other than solar PV,” says Mic Patterson, ambassador of innovation and collaboration at the Facade Tectonics Institute (FTI). “Wind is another familiar strategy, though its use in buildings has been limited. Thermal energy harvesting is another interesting strategy. A liquid piped through the facade system can harvest or shed heat, store it and deploy it when needed.” The various forms of adaptive facades are currently in a transitional state between the research and development (R&D) realm and broader commercial implementation. “It's an issue of adoption,” Patterson finds. “No innovation, regardless of how brilliant, is successful without adoption.”

TECHNOLOGIES WE ALREADY HAVE

“There is an opportunity for significant improvements in facade-system performance with the products that are on the shelf right now,” Patterson continues. Although he has long advocated more R&D in the field, the chief problem he sees at present is slow acceptance of technologies that are commercially available and known to be effective. High-performance buildings that meet or even exceed net zero energy and carbon metrics are already a reality, he says, with a caveat regarding scale. “If you look at the history there and the projects built to date, they're all smaller buildings,” he notes. “Most of them are single-story buildings or else low-rise. There are very, very few exceptions, and most of them succeed through rooftop-mounted PV.” Existing unitized curtain-wall systems, he says, including the variant known as the closed-cavity facade with a compact double-skin modular unit and shading devices sealed in the dust-free interior, dramatically improve a building's performance, yet in larger commercial buildings, too few owners have chosen them on account of cost, unfamiliarity, and other factors.

“Having a product is only part of the deal,” Patterson says; “you've got to have a supply chain to take that product all the way through installation and warranty, all the way through its service life.” For many owners, “faced with a new approach, a new product, [or] a new assembly strategy for the facade system, they'll go for the old tried-and-true one, in spite of the fact that it doesn't have as good performance because they associate it with risk.” Few people lose contracts or jobs over selecting an industry-standard product, and “current industry standard, unfortunately, is code-minimum.”

At the core of this reluctance to support the best-performing technologies, Patterson contends, is a common form of short-term thinking: “the tendency for these decisions to be made in a totally inappropriate context, which is first cost.” He points to large buildings in New York City that are now beginning their second century, yet many of today's owners continue to disregard the payoff from high-performing facade technologies beyond upfront costs or, at best, to assess energy-saving benefits over a compressed period of three years or so─and “society has to live with the results of this over the life of the building.” Today's new buildings, he says, may also stand for the next century or longer, and calculations of their facades' amplified performance should reflect that lifespan.

Other nations, he observes, are setting standards worth emulating in this area: “Europe has been in the lead when it comes to facade system development. Canada is ahead of the U.S., and I think the primary driver there is their weather is a little more severe.” Canada's national building code is evolving, and more progressive step codes in Toronto, Vancouver, and Montreal are driving energy-saving measures; New York, Seattle, and other American cities are moving in a similar direction. Still, “Adoption is the big problem; the industry, I think, is in a good position to respond to these things, and to some extent has responded, but you can understand their reluctance to invest in further R&D when the stuff that they've already developed is not being adopted.”