The largest international conference on architectural and solar glass is just weeks away, where Enclos will be represented by a team of seven innovators of building skin technology. Glass Performance Days (GPD) is held biannually in Tampere, Finland, with more than 800 participants from over 55 countries in attendance. This year’s program consists of two days of workshops and three days of conference proceedings over July 11-15.
Presentation topics by the Enclos team range from drain sizing over double curved surfaces, cassette systems, joint cost savings and energy gains from curtainwall systems, double-skin facades, and blast performance. In addition, Mic Patterson, Vice President of Strategic Development, and Jeffrey Vaglio, Associate Director at the Advanced Technology Studio of Enclos, will lead a workshop on Wednesday, June 12 entitled "Facades + Innovation." Patterson and Vaglio will be accompanied by Enclos’ James Casper, Senior Structural Engineer, and Michel Michno, Vice President.
The summit will feature over 180 lecture and poster presentations, and include 24 workshops. We hope you'll join Enclos and the leaders in building skin technology in Finland the second week of June.
The full program, including workshop descriptions and other conference details, is available at GPD’s website here.
Congratulations to Russ Boone for his nomination in The Ironworker magazine’s “IMPACT North America Safety Honors Program.” Boone, a Superintendent at Enclos, oversaw 160,000 man-hours of facade system installation without a single incident. He is a member of Washington, D.C.’s Local 5.
Rendering by the Advanced Technology Studio of Enclos
Installation of the new Hyundai Motor America Headquarters’ glass facade has reached substantial completion. Enclos is providing comprehensive design/build services for the six story, 504,000 square foot structure, which includes 135,000 square feet of custom curtainwall. The new $200 million headquarters in Fountain Valley, California is the largest investment in an office building ever made by Hyundai in the United States.
The project team is delivering Hyundai’s new headquarters as part of a fast-track schedule, with all trades participating to accelerate design, engineering and material procurement to accommodate scheduling goals. Completion is scheduled for late 2013.
Image by Cannon Design
The University of California San Diego Jacobs Medical Center has been recognized by ENR California’s 2012 Top Starts In California. The 10-story, 490,000 square foot hospital building is scheduled for completion in June 2016.
Architect Cannon Design created numerous curvilinear wall systems, including flat, segmented, curved and folded panel conditions that allow the wave-like structure to minimize traditional 90-degree building corners. Enclos is providing comprehensive design/build services for the project’s enclosure systems, including 205,419 square feet of curtainwall and 9,637 square feet of point supported structural glass wall.
"High-Performance Facades" is an ongoing series leading up to the Facades+ Conference in New York City, April 11-12. The theme of the two day event is performance. Part One is available here, Part Two here, and Part Three here. Part Four is the series conclusion. Join Enclos at the Facades+Performance Symposium and Workshops to continue the high-performance dialogue.
by Mic Patterson and Jennie Matusova
The path to a high-performance facade is simple in concept. In addition to the facade fundamentals — weather barrier, air and water seal, condensation resistance, safety and comfort — the high performance facade must succeed in doing the following:
- Optimize daylight to reduce energy consumption and cooling load from electrical lighting.
- Optimize view to provide a connection to nature.
- Minimize glare.
- Control solar heat gain.
- Minimize heat loss in cold climates.
- Provide natural ventilation to the greatest possible extent.
- Optimize performance and minimize environmental impact over the lifecycle of the facade system.
The complexity comes in the implementation of these provisions, a delicate balancing of often contradictory considerations. And that’s just the beginning.
The context of high-performance facades was discussed in Part One, with a working definition adopted in Part Two, and relevant performance attributes explored in Part Three. This final, in-depth article aims to cut through the ambiguity of building facade performance and identify key metrics and best practices appropriate to the development of high-performance facade systems. The issues are many and complex, and although a fully detailed assessment is well beyond the scope of this report, additional resources are provided for reference in further research.
High-performance buildings and systems yield from high-performance processes: design, material procurement, fabrication, installation, commissioning and maintenance. High-performance design encompasses optimization of the attributes identified in Part Three over the building lifecycle, but high-performance attributes developed in design can easily be compromised during manufacturing and installation phases. A commissioning process helps assure that systems are operating as designed, and maintenance procedures are required to sustain performance levels over the lifetime of the building systems and assemblies. The following sections break down the various components and considerations that should be addressed at each stage of the design.
A Foundation For Performance
Basis of Design (BOD): This narrative becomes the roadmap to attaining building performance goals. Establish key performance benchmarks early as part of the BOD, including relevant green standards and rating systems (Energy Star, LEED, Green Globes, Living Building Challenge). Identify where code, standards and rating system requirements will be met or exceeded. Address how the facade systems will contribute to achieving these benchmarks as part of an integrated whole building design. These benchmarks become the building and system’s performance goals.
Project Delivery Strategy: Adopt a project delivery strategy suited to the goals of a high-performance building project. The conventional design-bid-build strategy is generally inappropriate for this project type. Rather, consider design-assist, integrated project delivery, or other collaborative processes that facilitate the involvement of appropriate constituents early in the design process.
Service Life: Define a design service life for the building and the facade system. Assure that the estimated service life of the building, facade system, materials and subassemblies of the facade system are commensurate. ISO 15686, CSA S478-95.
Durability & Maintenance Plan: Adopt or develop a durability and maintenance plan for the facade system that supports the design service life. In addition to maintenance requirements, the durability plan should define major renovation cycles over the building lifespan. The Canadian version of LEED provides a point for durability planning.
Operating Manual: The operation of a high-performance building is often a complex affair placing demands on the facility’s engineering team and building occupants. Operational procedures should be developed simultaneous of design development. Training strategies should be included.
Facade Commissioning: Commissioning is a process of assuring that the building owner gets what they ordered, and that it is performing per specifications. While the proof of performance is achieved near the time of project completion in most cases, the planning and process itself must start early in design. See more on commissioning in Proving Performance below.
An integrated design process requires that facade design be coordinated and linked with other building systems to achieve whole-building performance goals. It is a collaborative design process that requires the early involvement of all relevant constituents. The process commences with fundamental considerations of:
- building use
- site conditions and characteristics
These considerations are used in determining:
- building orientation. Conditions will vary for each exposure of the building façade, where each elevation should be considered separately and its design varying accordingly.
- materials, assemblies and systems design, including glass specification, material finishes, framing system design and shading systems. Virtually all aspects of the building facade are designed within the context of a building’s specific climate, site and use.
Whole Building Energy Modeling: Should be mandatory for high-performance building designation. Must be developed early in the process and used as a basis for decision making during schematic design and design development.
Window to Wall Ratio (WWR): With existing glazing technology, vision glass areas of over 30 to 35% impose unnecessary energy burdens on a building. In most cases this glass area is adequate to provide optimal daylighting and view. The common occurrences of much larger WWR in today’s buildings are aesthetically and financially motivated (highly-glazed buildings produce higher occupancy and lease rates, a fact supported by any developer of premium commercial buildings). New glazing technologies may solve this problem, but likely at a considerable cost premium throughout the foreseeable future. Unless a highly glazed building is achieving near carbon neutral net-zero energy performance, a claim of green high-performance in such a building is arguable.
Daylighting Design: Should be mandatory for a high-performance building designation, using metrics from IES LM-83 to maximize daylight, minimize direct solar penetration and prevent glare. The daylighting collaborative is another resource.
Budgeting & Cost Analysis: Performance has cost implications. It is imperative that an appropriate context be created for evaluation of cost, or performance-enhancing features will either not develop or risk being lost to value engineering. First-cost or short term payback cost analysis will seldom support high-performance features. Lifecycle Costing Analysis (LCCA) is the appropriate methodology.
Aesthetics: The building skin impacts both performance and appearance like no other building system. The building design should respond to the context of local culture and neighborhood in its appearance and connection to neighboring public space. Large projects often include architectural artworks. Art glass in the building facade, as seen at the UCSF Medical Center at Mission Bay, is a recent example.
Lifecycle Assessment (LCA): Environmental impacts should be evaluated throughout the decision-making process of schematic design and design development. LCA tools and processes facilitate this evaluation and provide for the consideration of embodied energy and end-of-life impacts. LCA is relatively new and still evolving. Current techniques are somewhat subjective and it remains an inexact science owing to the enormous complexity of the undertaking, but lifecycle inventory data is growing, and new simplified tools are emerging that provide for the integration of LCA in early design processes. Tools include:
Adaptability & Disassembly: Design for future adaptability to changing building use. Plan for facade disassembly, recycling and disposal at end-of-life. Account for resulting cost, energy consumption and environmental impacts. The CSA Group offers a guideline for the design of adaptability and disassembly in buildings.
Health & Safety
A growing body of evidence documents the productivity enhancements provided by a healthy and comfortable indoor environment, an attribute providing a tremendous but often unrecognized financial benefit to a business enterprise as well as the health benefit to the employee.
- Thermal: Model MRT (mean radiant temperature; area-weighted average temperature of all surfaces) to evaluate thermal comfort of interior spaces.
- Acoustical: STC and OITC are the most common rating systems.
- Glare Analysis (interior and exterior): Metrics for glare analysis are emergent. Building designs with large WWR should require exterior glare analysis to avoid the kind of problems experienced by the Walt Disney Concert Hall, Vdara Hotel and Nasher Museum, especially if there is concave curvature to the facade.
- Interior Light Levels: Use IES recommendations as appropriate to workspace function.
- Indoor Air / Environmental Quality: Americans spend approximately 90% of their time indoors, making indoor air quality a primary concern. EPA IAQ. The forthcoming LEED v4 includes a major indoor environmental quality section.
Biophilia: Provide connection to nature through the provision of ample daylight, view and natural ventilation.
Security Analysis: The extreme loading conditions that may result from storm winds and blast loads are important considerations in facade design. Advances continue in the area of blast load facade engineering. Impact resistant specification criteria have developed in response to hurricane force winds, best represented by the South Florida Building Code with attention to glass in the building facade. Mullions are also addressed. Forced-entry at the accessible areas of the facade must be anticipated and prevented. TAS 202 covers testing procedures for windows and ground level glass systems. Similar requirements and procedures are migrating up the eastern seaboard in the wake of recent super-storms.
Resilience: Storm effects are increasing in parallel with storm strength in a pattern of rapid climate change. These effects must be anticipated and accommodated in building design such that buildings remain operational in the aftermath of super storms.
U-Factor: Work with assembly U-factor rather than other metrics such as center-of-glass U-factor.
Glass: To optimize thermal performance use double or triple glazing, strategically placed spectrally selective low-e coatings, gas fills, nanogels for non-vision lites, and warm-edge spacers. Look for vacuum glass as a future high-performance product.
Wall Panels (opaque, translucent): Provide thermal breaks, adequate insulating material, backpans and carefully engineered shadowboxes to optimize thermal performance and CR. Consider the use of vacuum insulated panels (VIPs).
Insulated glass units (IGUs) are highly engineered products of increasing diversity with complex behavior and appearance attributes. The appropriate application of these products in the building facade is an escalating challenge to the design profession, but pivotal to the success of contemporary highly glazed buildings. The issues are only briefly addressed here.
U-Factor: Thermal insulation metric, lower is better. High-performance double-glazed IGUs are as low as 0.30; triple-glazed as low as 0.13 (in combination with low-e and gas fill as described following). Use minimum 0.30, and buy as low as budget can support (note: use whole assembly value, not center of glass).
Solar Heat Gain Coefficient (SHGC): The fraction of incident solar radiation transmitted and absorbed as solar heat gain (a number between 0 and 1). The lower the number, the lower the solar heat gain — typically in the range of 0.20-0.50. Commercial buildings characteristically have high internal heat gain and consequently utilize low solar heat gain glazing even in colder climates. If the building energy design incorporates a passive solar heating strategy, higher SHGC values will be preferred (again, use whole assembly value, not center of glass).
VT/VLT (visible transmittance/visible light transmittance): the percentage of incident light transferred through a glazed assembly or the glass itself, respectively. Optimal daylighting and view often involves the attempt to balance high VT with low SHGC.
Condensation Resistance (CR): An NFRC rating on the scale of 1 to 100, with 100 being the highest corrosion resistance. Most consultants recommend a rating of at least 50 for window products. The design of high-performance facade systems should include rigorous thermal and condensation analysis to assure no condensation under predicted interior and exterior environmental conditions (additional information here).
Low-e #2 / #3 Surface: In commercial glazing, where limiting solar heat gain is the predominant concern, the #2 surface is preferred.
Low-e #4 Surface: Can be used in combination with low-e on #2 surface to produce U-factor approaching 0.20. However, CR is reduced because the prevention of radiative heat transfer from the interior leaves the glass surface colder. Warm-edge spacers will help, but careful analysis is required to identify cold spots where condensation may occur. Note that the #4 surface represents the interior surface.
Gas Fill: Consider the use of less conductive gasses, such as argon, in place of air in the IGU cavity.
Warm-Edge Spacers: The metallic edge spaces typically used in IGUs to separate the glass lites are a weak link in the assembly. They act as a thermal bridge resulting in panel edge temperatures much lower than center of glass. Condensation and heat loss may occur in this area (additional information).
Triple-Glaze, Low-e, Gas Fill (consider as cheaper alternative to double-skin system, unless part of a natural ventilation strategy).
Future Tech: Vacuum glazing, U-factor approximately 0.08.
See a definition of these terms and much more here:
Easily accessible and useable tools are provided free by the LBNL.
The frame of a curtainwall system can easily amount to 5-10% of facade surface area. The frame incorporates the air and moisture barrier, and may act as a thermal bridge between inside and out, significantly compromising the U-factor of a facade assembly.
Thermal Bridging: Aluminum is highly conductive. Provide full thermal breaks, especially in climates with a cold weather season as experienced in northern Europe, northern United States and Canada to prevent heat transfer and condensation on interior surfaces.
Typical air infiltration would be 0.06 CFM/sqft at 6.24 PSF static pressure (AAMA 501.1 / ASTM E 331).
Typical water standard would be no uncontrolled leakage at 15 PSF static and dynamic (ASTM E 283).
Glass Makeup: Strategically located frits, spectrally selective and low-e coatings, blinds in the IGU cavity, dynamic glass (electrochromic, thermochromic, photochromic).
Shading Devices: Exterior is the best location to block heat gain, but results in maintenance issues because of exposure. Horizontal shading is best on the south exposure, and vertical best on east and west exposures (northern hemisphere). Interior shades and blinds are good for glare control, but too late for solar control. Instead, use split shades so the upper section can be used independently to bounce light deeper into the room while the lower section is used for glare control. Double-skin facades are sometimes used to provide a protected cavity for a shading system. Shading components in a double-skin cavity or IGU cavity may cause undesirably radiative heat gain.
Ventilation Scheme: Operable windows and vents are an opportunity to substitute natural ventilation for mechanical cooling, thereby improving interior air quality and reducing energy consumption. Mechanical cooling may be entirely eliminated in some climates. Double-skin designs may facilitate natural ventilation strategies. A good performance metric is the percentage of the year that a building can be naturally ventilated, albeit a climate dependent metric, but one for which local benchmarks can be identified or established. The Tower at PNC Plaza, designed by Gensler with the aim of being the world’s greenest building, is intended to be naturally ventilated for over 40% of annual work hours.
General Design Considerations
Consider the use of dynamic glazings and shading systems as a means to tune such things as VLT and SHGC in response to changing environmental conditions.
Building Integrated Photovoltaics (BIPV): Consider BIPV as a means to offset building energy use, but only after all efficiency measures have been optimized.
Structural Design: Wind, seismic, impact and blast. Embrace resilient design practices that anticipate escalating natural and social forces.
Constructability Review: Provide ongoing evaluation throughout the design process of the impact of design decisions on fabrication and installation processes.
Pre-Construction Performance Mockups: Test typical conditions of each major wall type and their interfaces in the form of full-scale mockups. Do not skimp on the mockup program. Test protocols per ASTM E2099 – 00(2007) and related specifications. Visual mockups are becoming increasingly as common as the materials incorporated in the growth of facade in diversity. Test protocols per ASTM C 1036.
Field-Testing Water & Air Infiltration: Post-construction field-testing is becoming increasingly common. Tests involve representative portions of the constructed façade, conducted in accordance with the requirements of AAMA 501.2 and AAMA 502.2.
Commissioning: Building facade commissioning is also trending as facade systems incorporate increasing complexity. Dynamic systems with sensors, controllers and operable shading devices, integrated with lighting systems and the building management system need the performance validation that commissioning provides. LEED provides points for one-time commissioning and additional points for a program of ongoing commissioning.
Post Occupancy Monitoring & Data Dissemination: This is desperately needed to demonstrate the effectiveness of current practices so that refinements can be made going forward. In the too few instances where such data is collected, owners are reluctant to publish it. Codes, standards and rating systems must embrace this and require proof of performance during the operational phase of a building. Cities like New York and Minneapolis are now requiring the publication of building energy consumption data.
Consider lifecycle environmental impacts to inform the design development process, material and product selections. LCA provides the context for sustainable building practices, including material and energy consumption throughout the process from extraction to transport, manufacturing, construction, operations, maintenance, renovation cycles, and finally, disassembly and recycling/disposal.
Durability & Adaptability: Design for long building life. Considering the magnitude of the investment of resources represented by large commercial and multi-story residential buildings, they should be designed for long service life. This necessitates the anticipation and accommodation of the changing patterns of future building use and function. Longer building service life is an inherently sustainable attribute, but also exposes the building to the potential of additional cycles of changing use.
Simplicity: Use the simplest available option. Simplicity is an undervalued principle in the design of high-performance buildings, which are trending towards escalating complexity. This complexity must be evaluated in the context of sustainability: will these increasingly high-tech strategies contribute to the sustainability of the built environment? Some will, some will not. The attribute of durability, for example, is sometimes neglected in the evaluation of high-tech design practices and building assemblies. Consider passive design strategies for thermal control and natural ventilation.
Ultimately, sustainability is not determined at the level of an individual building, but buildings must contribute to the sustainability of the higher order systems of community, region, nation, and ultimately, planet.
Unsurprisingly, the implementation of a truly high-performance building is no easy feat. This article barely scratches the surface of the considerations relevant to the building skin alone. Energy efficiency, the most frequent focus of building performance, is not enough by itself. In order to truly earn a high-performance building designation, all of the considerations identified above must be considered and addressed in an integrated response to the building program.
About the Authors:
Jennie Matusova is a designer at Zaha Hadid Architects in London. She received a Bachelor of Architecture and Minor in Communication Design from the University of Southern California, where she graduated Cum Laude with a thesis award for "Outstanding Independent Research" on architecture and crime.
© enclos corp 2013