FORWARD FACING: Innovations that are Moving Building Enclosure Design, Fabrication, Installation and Performance in Bold New Directions  

Building design continues to evolve as they are pushed by owner desires, code requirements, and computerized design capabilities. This is most evident in the building enclosure systems which include building facades, fenestration, and roofing systems. All of these have grown more and more complex and are typically less forgiving in order to meet demands for energy performance, occupant satisfaction, cost requirements, and durability over time. Therefore, it is incumbent upon architects to stay up to date with emerging technologies, products, and systems that are available for optimizing performance while satisfying client and design needs.

Building Enclosure

Over the past decade, the growing significance of building enclosures has been evidenced by the increased attention being paid to this topic by design professionals. Some of this is the result of a joint effort between the National Institute of Building Sciences (NIBS) Building Enclosure Technology and Environment Council (BETEC) and the American Institute of Architects (AIA) who signed an agreement in 2004 to establish the Building Enclosure Council (BEC) initiative. Currently, more than 3,000 affiliated architects, engineers, contractors, manufacturers, and others with an interest in building enclosures participate in Building Enclosure Councils (BECs) around the country in 26 chapters representing both cities and counties. These BECs promote the exchange of information and encourage discussion on matters concerning the products, systems, and science used to enclose buildings. Further, they address related topics such as training, education, technology transfer, weather conditions, and local issues. As a resource to this effort, NIBS, under guidance from the Federal Envelope Advisory Committee, has developed a comprehensive guide for exterior envelope design and construction for institutional and office buildings. Known as The Envelope Design Guide (EDG) it is continually being improved and updated through the BECs.

A recent development in the work of the BETEC is the creation of a NIBS Guideline for the Building Enclosure Commissioning Process (BECx). This effort recognizes that, just like other critical elements of a building, an independent review or commissioning process is an impartial way to see that the design and construction of facades, fenestration, roofing, etc. are all carried out and tested appropriately to perform as intended. As stated in the document, this “Guideline provides recommendations for navigating the enclosure commissioning process from its necessary inclusion in project planning to its continued emphasis throughout the life of a building. The Guideline is intended to be usable by all owners for all building types.” Regarding the process, it goes on to point out, “The Building Enclosure Commissioning (BECx) process is utilized to validate that the design and performance of materials, components, assemblies and systems achieve the objectives and requirements of the owner. The BECx process achieves this through experience, expertise, modeling, observation, testing, documenting and verifying materials, components, assemblies and systems to validate that both their use and installation meet the owner’s requirements.” Those interested in assuring proper building envelope performance will be well served by using this document and process.

In light of this trend for better performance while still meeting other client and user demands, we will look at eight items that can help architects create building enclosures that perform better, look better, and remain within budget and schedule.

Insulated Metal Panels

Insulated metal panels used in an exterior wall or facade can provide vast design opportunities while helping to meet sustainability performance goals. Indeed, they have been a common and popular choice by many architects in order to build more energy-efficient buildings while keeping within budget and material requirements. In practice, these systems are commonly provided by a single manufacturer to provide an insulated metal back-up panel that is also an air, water, thermal, and vapor barrier panel. Typically, this panel is installed in a horizontal orientation completely outside the structural supports. This way, there are no thermal bridges to reduce the energy efficiency of the wall. Then a final facade finish of choice can be installed as the exterior weathering skin. High-performance continuous insulation systems like this help commercial and industrial buildings meet energy codes and standards like ASHRAE 90.1. As a metal product, the commonly high level of recycled content makes it an environmentally friendly choice for architects, designers, builders, and contractors seeking a sustainable product.

It is common to think of insulated metal panels like this as only used with a metal skin, which is certainly a common option. However, they can also be used behind any type of facade cladding, including masonry or other materials. The benefit is that these manufactured wall panels have the potential to save time and money since they provide, in a single step, air, water, thermal, and vapor protection for a facade.

Craig Caudill, EVP of a construction company known as ProClad in Noblesville, Indiana notes, “Insulated metal panels are ideal for exterior wall systems. They provide not only easy installation and great cost savings over other types of systems, they also have great efficiency in controlling temperatures due to their continuous insulation. And the installation of the panels involves only a single trade.”

Three-Dimensional Aluminum Composite Panels

Another popular cladding choice for commercial buildings, particularly in retail and office applications, is the use of aluminum composite panels. These exterior skins are more rigid and self-supporting than metal siding due to their multi-layer makeup of an inner and outer metal face separated by a very thin layer of rigid foam or other material. This composite construction means that the appearance and shape can be controlled with less likelihood of warping or “oil canning.” A smoother appearance makes them particularly well-suited for modular panels over an insulated underlayment to act as the weathering and appearance surface of a building facade.

Recent innovations in the manufacture of aluminum composite panels has allowed for bold new looks to be realized. Rather than keeping the panels as flat surfaces, fully three-dimensional panels are now available that have either a convex or concave shape. The innovative 3D shape adds visual and textural interest to the facade of a building by creating a true and intentional depth to the panels. Further, the panels are available as part of an overall system that allows for installation either in new construction or on existing buildings.

As a complete system, care is taken not to produce any wasted material because of the size of the modular panels. There are a number of different sized modular panels available in both convex and concave configurations using the minimum waste approach. This engineered manufacturing process creates a systemized, unitized product that can be used as a kit of standard sized panels allowing designers to work with many different arrangements and layouts. Further, one of the benefits of aluminum is that color choices are numerous with new ones often available regularly. It also means that accent bands or distinct colored areas can be designed easily within the modular arrangement. The net effect is a structurally rigid 3D panel system that provides for a colorful, undulating visual effect especially under dynamic lighting conditions.

Attaching the panels is typically achieved using standardized attachment systems. Some allow for simple snap-in-place possibilities while others are based on a removable design making it possible for subsequent changes to be made easily to the exterior facade. Either way, 3D aluminum composition panel systems have been tested using ASTM 330 “Standard Test Method for Structural Performance of Exterior Windows, Doors, Skylights and Curtain Walls by Uniform Static Air Pressure Difference.” Under the procedures of this test, the 3D panels have performed impressively at over 135 psi. Manufacturers indicate that they are durable and offer a 20- to 30-year finish warranty. Henry Bilge, CEO of ACPExpress notes, “Three-dimensional aluminum composition panels have been developed as a world-class product for exterior cladding.”

Textile Facades

An alternative to rigid metal or other materials used on facades is to take a different approach that relies on an open mesh material to create the visual outer appearance on a facade. Known as textile facades, they are a relatively new concept in the United States but have been used for some time elsewhere. To be clear, they are not usually a cloth textile, rather, they are made from a flexible composite material, but the term textile facade has become the generic way to refer to them. “While textile facade usage is common in other parts of the world, the United States is just now discovering the many benefits of its use,” says Jim Driggs, Serge Ferrari North America’s Business Development Manager.

There are a number of good reasons to consider using textile facades, not only for aesthetics, but also to improve the overall building performance. They are incredibly versatile, lightweight, flexible, printable, and 100 percent recyclable. As a shading device installed over windows, they can improve thermal comfort by reducing the heat load on the building. They also provide visual comfort by reducing glare without obstructing the view to the outside. With mesh openings on the order of 20 to 30 percent, they still allow natural ventilation to pass through while adding a degree of privacy and visual screening for windows.

Textile facades can be used on retrofits as well as new construction as a lightweight and cost-effective alternative to traditional cladding materials. They can be a minimally invasive way to cover large spans and dramatically change the overall appearance of a building, either as a continuous cover or in smaller modular panels- vertically, horizontally, or in 3D configurations. They can be installed in tensioned fixed frames or even be retractable. The flexible composite materials can easily achieve complex curvatures, making design possibilities virtually limitless. The material can be digitally printed for artistic or branding opportunities or images can be projected onto them. Integrating LED lighting can also dramatically transform the appearance, especially at night.

Composite mesh can be specified in a broad spectrum of designer colors, to be UV stable, with anti-mold and anti-mildew treatments. It can also be flame retardant as well as non-combustible. A 10-year warranty is available with a 20- to 25- year life expectancy being common. At least one manufacturer ensures exceptional dimensional stability and flatness with no re-tensioning required with a smooth finish that requires very little upkeep.

Exterior Finish Options

By now, it is becoming clear that while facades are an integral part of the building enclosure and need to be treated properly from a performance standpoint, the aesthetic and finish options can be quite varied, even endless. This is true in terms of colors and textures, but it’s also in terms of how the finish maintains itself over time.

An emerging trend is to specify and use self-cleaning and heat-reflective finishes on building facades. Such finishes help the building maintain its original look since they are formulated to be cleaned time and time again with rain water. As water hits the surface, it simply beads off the exterior and takes any dirt, grime, or soil in its path with it. Further, some of the same finishes use a mix of raw materials specifically chosen to reflect the sun’s heat and ultraviolet (UV) rays, thus lowering surface temperatures, reducing heat island effects, and saving energy. When used over continuous insulation or an exterior insulation finish system (EIFS), the whole system is more effective at stopping thermal bridging and meeting current and anticipated energy codes.

The self-cleaning and heat-reflecting properties of exterior finishes can be an important means to help buildings look and perform better over time. They can also help owners effectively manage their buildings better since ongoing maintenance costs can be much less compared to traditional finishes. Environmentally, at least one manufacturer uses a photocatalytic technology that helps break down atmospheric pollutants in the air and on the surface. These same photocatalytic properties are what help keep the wall surface temperatures cool as it reflects heat from the sun. Ideal applications for this type of finish include new construction or refinish projects over EIFS, stucco, masonry, or concrete substrates.

Silicone-Based Air Barriers

An important part of any exterior wall assembly, which is also mandated by building codes, is an air and water resistive barrier. There are numerous products on the market available to address this but one of the most effective, especially for larger buildings, is to use a spray- or roller-applied silicone coating over an appropriate substrate. One of the better known types is a one-part, liquid-applied elastomeric coating that cures to form a flexible, vapor-permeable membrane. This water-based silicone air barrier may be readily complemented by a fully compatible high-performance array of compatible products for addressing edges, seams, openings, and other common construction conditions.

A key characteristic of silicone air barriers is their ability to prevent air and water infiltration but retain the ability to “breathe” by allowing trapped moisture or water vapor to escape. This attribute mitigates concerns about potential corrosion and mold growth caused by moisture trapped inside wall assemblies. Of course, during construction, this same material needs to be able to handle exposure to the elements, particularly sunlight and potentially harmful ultraviolet (UV) radiation and products are available to meet that need. Similarly, the material needs to tolerate temperature differences during construction allowing applications in a range of conditions. At least one such product has been tested and found to be capable of successful installation in temperatures as low as 20°F (-6°C).

In addition to the spray-on air barrier, the other products of a complete system typically include sealants and flashings to properly cover and seal the locations other than the flat surface of a substrate. This includes compatible and primer-less liquid silicone flashing at window and door openings, silicone sealant along joints or seams, and silicone transition strips for plane changes or corners. Together, this proven, coordinated system of compatible products provides long-term durability for the building enclosure while helping to improve the thermal and weathering performance of facades.

Fenestration Systems

Virtually all building facades incorporate some form of fenestration, and most architects spend a good deal of time sizing, arranging, researching, and specifying it–all for good reason, since there are many ongoing advances and trends in window fenestration systems. Improved energy efficiency in particular continues to be one of the strongest trends and one most likely to endure as driven by client needs and building codes. Manufacturers have responded by developing new fenestration products and installation methods. Architects are specifying improved thermal barriers in aluminum window, storefront and curtain wall systems, selecting more energy-efficient glass with many varieties of low-E coatings or triple glazing, incorporating many different types of glass on the same building, adding exterior sunshades and interior light shelves, and trying out self-shading electrochromic glass. One specific response to this energy performance trend is the availability of wood and aluminum-clad wood windows with triple glazing and optional krypton gas that achieve exceptional thermal performance with U-Factors as low as 0.16.

Window trends aren’t limited to new construction. More and more existing buildings are being renovated in a way that respects their historic character while incorporating the latest fenestration technologies, including new materials, more energy-efficient glass, and new muntin options. Sometimes historic preservation mandates dictate that the existing windows be replaced with windows of the same material as the original windows; in other cases, the original windows are replaced with new materials and muntins. Either way, the goal is the same–preserve the original character of the building as expressed in the fenestration appearance, but update the performance to meet current needs.

The rigors of budget and schedule come to play regardless of building type or age. As a result, there is an increasing desire for fenestration systems that are factory-engineered and pre-glazed to expedite installation during the construction phase. Of course, there is also a desire to be more creative in building designs, resulting in increasingly complex facade systems with many plane changes, large expanses of glass, offsets, corners, tilts, glass types, spandrels, curved glass, etc. The key to a successful fenestration solution is to understand all of the options available and strive for an appropriate balance between design and performance.

Storefront and Curtain Wall Systems

While we have looked at fenestration in general, let’s look a little closer at two common commercial facade systems, namely storefront and curtain wall systems. Storefront systems take their name from retail settings, where they are commonly used for large, single-floor height openings of glass. These systems are intended for light commercial single-story retail viewing and readily incorporate doors and entrances for quick access to interior product displays. They are also often used in other commercial, educational, and institutional settings as well. They typically span a floor-to-floor or floor-to-head condition without passing in front of any intermediate anchorage conditions. Most storefront designs utilize small, non-obstructive, aluminum framing shapes that can present a “flush glass appearance” where glass seems to disappear into the framing system. They are available in a range of standard component sizes and hardware options with glass thickness choices ranging from ¼-inch to a full 1-inch insulating glass.

From a performance standpoint, storefront systems can be looked at in terms of structural capabilities and thermal performance. As a light commercial system, storefront systems are typically limited to a maximum height of 12 feet due to the capacity of the framing and glazing system. Thermally, storefront systems can provide adequate performance. It is important when specifying materials or components for exterior facades to call for appropriate thermal breaks in the framing and glazing support systems. It is also necessary to select the highest-performing glass available that is appropriately coated and treated to meet the thermal needs of the building in its particular climate location. Fortunately, most storefront manufacturers now offer a full range of choices in this regard so performance targets can be incorporated and met.

Curtain wall systems are generally designed to meet higher performance standards than storefront systems since they are often exposed to harsher conditions. As a complete, multi-story exterior envelope facade system, they provide a non-structural, relatively lightweight, weather-tight covering on buildings. They impact the design appearance of the exterior of course, but it is their superior performance and carefully engineered assembly that often make them an attractive facade solution. In the case of small, low-rise projects, the system may be field fabricated or “stick built” and glazed using standard components similar to a storefront system. For larger, multi-story projects with repetitive and large-scale surfaces, pre-fabricated and factory glazed or “unitized” systems may be warranted to create a monolithic assembly. In either case, curtain wall systems are generally installed outside of the structural system of a building running past floor slabs and other structural elements. They are then attached via tiebacks directly to the building structure at floors, columns, and beams. This installation process means that all excess wind loads and dead loads imposed on the fenestration system are compartmentalized and transferred directly to the building structure. Hence the curtain wall system carries only its own weight and loading while the building structure absorbs all imposed loads.

Since the structural performance of curtain wall systems is based on transferring loads to the building structure, their size is virtually unlimited horizontally or vertically as long as the building is designed to carry the transferred loads. From a thermal performance standpoint, curtain wall systems are typically capable of superior thermal results based on meeting higher wind pressure ratings, tighter seals against weather and more attention to glazing options. The material of choice is aluminum with manufacturers offering anodized finishes ranging from clear to earth tones including tans and blacks. There are also numerous painted colors available with 10-year standard finish guarantees.

Single-Ply Membrane Roofing

Building enclosures include all sides of a building including the roof. Of course, in some creatively shaped structures, it is sometimes hard to discern where the facade ends and the roofing begins from a design standpoint. In terms of performance, they should both provide equal protection and create the appropriate barriers for thermal, weather, and air infiltration. While there are many well-known roofing systems available, one is garnering some increased attention even though it has been around for more than 35 years with greater than 99 percent of the installations still performing quite well. It is based on a single-ply membrane made from Ketone Ethylene Ester or simply abbreviated as KEE.

KEE roofing membranes are appealing for several high-performance reasons. First, they are made from the roofing industry’s heaviest base fabric offering superior puncture and tear resistance. Second, the KEE content allows the roofing membranes to maintain excellent flexibility, as well as chemical and UV resistance. Finally, their quality can be ascertained by meeting or exceeding the requirements of ASTM D6754-02 “Standard Specification for Ketone Ethylene Ester Based Sheet Roofing.” Beyond roofing, they are also well suited as a waterproofing membrane for below grade facade applications.

From a sustainability standpoint, KEE membranes have several other desirable attributes which may contribute to LEED points and credits. Available in white reflective colors, it allows the roof surface to reflect solar and ambient heat, which can significantly reduce air conditioning costs in the building where it is installed. It can also help prevent heat island effects often caused by dark-colored surfaces. As an environmentally friendly product, it contains no volatile organic compounds (VOCs) and works well with green roof systems. Since it is compatible with asphalt, it allows re-roofing over built-up roofing systems, thus eliminating the need to tear off and dispose of existing roofing materials. Finally, it possesses a long life cycle as a durable material with high resistance to chemicals, air conditioning coolants, jet fuels, restaurant grease, UV light, airborne bacteria, acid rain, and industrial pollutants.

CASE STUDIES

Conclusion

The art and science of building enclosures, particularly in building facades and roofing, continues to evolve. Staying abreast of imposed requirements and demands as well as industry-wide developments in products and technologies allows architects to create new or renovated buildings that provide exceptional performance while still satisfying all other design criteria. Constructed and installed correctly, the high-performance solutions presented in this article can also help assure long term durability and satisfaction from the owners and occupants of those buildings.

Peter J. Arsenault, FAIA, NCARB, LEED AP is an architect and green building consultant who has authored more than 100 continuing education and technical publications as part of a nationwide practice. www.linkedin.com/in/pjaarch