Executive Summary

There is a significant and growing interest in the use of highly-glazed façades in commercial buildings. Large portions of the façade or even the entire façade are glazed with relatively high transmittance glazing systems, and typically with some form of sun control as well. With origins in Europe the trend is expanding to other regions, including the United States. A subset of these designs employ a second layer creating a double envelope system, which can then accommodate additional venting and ventilation practices. The stated rationale for use of the these design approaches varies but often includes a connection to occupant benefits as well as sustainable design associated with daylighting and energy savings. As with many architectural trends, understanding the reality of building performance in the field as compared to design intent is often difficult to ascertain. We have been particularly interested in this emerging trend because prior simulation studies have shown that it should be technically possible to produce an all-glass façade with excellent performance although it is not a simple challenge. The published solutions are varied enough and sufficiently complex that we undertook a year-long international review of "advanced façades" to better understand the capabilities and limitations of existing systems and the tools and processes used to create them. This is also intended to create a framework for addressing the missing tools, technologies, processes and databases that will be needed to turn the promise of advanced façades into realities. This summary, available as a PDF file and a web site, reports those findings. 

At the beginning of this scoping study, our initial impression or reaction to this architectural trend toward all-glass transparent façades was objectively critical. The concepts and claims were impressive, particularly those being applied to double-skin façades. Ventilation concepts, dynamic shading, and daylighting were being used to achieve improved indoor air quality, energy efficiency, thermal comfort, and occupant performance. Many of the building physics concepts discussed were not new; in fact, they have been advocated by researchers for decades. The difference was that these concepts were being applied or wrapped in a new design aesthetic. Why now? What was instigating this architectural trend? Were the architects and engineers who worked behind the scenes actually realizing their performance goals? Our questions stemmed from our in-depth knowledge of just how difficult it is to properly engineer these advanced façades. For many of these concepts, there are many unknowns: optical and thermal modeling of these systems is not routine, and coupling heat transfer and air flow from an isolated façade system to the whole building is complex. In addition, we wondered how clients were able to afford and justify the increased design, materials, and construction costs for these complex façades when in most of our experience, the financial bottom line was always pointed out as the determining factor. 

Our work began by sorting out the various building physics concepts being applied to buildings touted by the architectural press. Many of the descriptions were garbled or incomplete. Some were counterintuitive or downright confusing. We compiled a list of the concepts being applied to these advanced façades and described how these technical concepts were being realized in typical commercial buildings. With one-on-one interviews and a roundtable discussion, we then looked into what is involved with the design, engineering and implementation of such systems. How were architects and engineers able to convince clients to use these advanced façades systems despite increased costs? How were others able to jump the cost barrier? Our interviews revealed the differences in life-cycle economics between the U.S. and Europe. We also reviewed the design tools used to engineer and evaluate the performance of these systems, specifically the thermal and daylighting tools as related to building energy use and occupant comfort. Some of the fundamental limitations of these tools were reviewed. Finally, we performed a literature search to find third-party studies on how these buildings performed after they were built. It was extremely difficult to find any objective data on the performance of actual buildings, particularly double-skin façades and adaptive façades. Several detailed building case studies are given with information based on published architectural press articles. Links to other building case studies are also given. 

At the conclusion of this scoping study, we have gained an appreciation and better understanding of this new trend towards all-glass façades. In Europe, there is an earnest attempt to achieve high-performance using advanced façade concepts. In the U.S., architects and engineers are further behind but remain interested in pursuing the stated overarching environmental and performance goals. There remain several critical needs that must be satisfied before such systems can be routinely engineered. Design tools must provide enhanced power to accurately model complex integrated building systems but paradoxically must be made easy to use in the early design process. Algorithms to model optically complex façade elements must be developed and validated, as must airflow models for large cavity façade systems. A variety of thermal coupling strategies between the façade and the whole building must be adequately simulated. Simulation code to test and develop control algorithms for dynamic systems must be made more available, robust and open. Regulatory standards and procedures for rating complex advanced façades and demonstrating compliance with local energy codes must be modified to more easily accommodate these complex systems. Post-occupancy, third party monitored data must also be collected, analyzed and made available to the architectural community in order to better understand and improve upon the performance of these systems. Architectural design guidelines and building case studies will help architects and owners better understand the applicability of various concepts to their specific building projects. 

The field of advanced façades is a rapidly evolving work-in-progress. We invite readers to contact us with information on the subjects described above, at ESLee@lbl.gov

Question/Information: eslee@lbl.gov