21st Century Building Envelope Systems: Merging Innovation with Technology, Sustainability, and Function

By addressing energy efficiency, moisture infiltration, aesthetics, and occupant comfort, building envelope elements and component systems enhance design opportunities and minimize potential risk

Barbara A. Nadel, FAIA

"The building envelope is more than a façade−it is the poetic mediation between an internal spatial realm and the outside world."
-Antoine Predock, FAIA, 2006 American Institute of Architects Gold Medalist
Antoine Predock Architect, PC, Albuquerque, NM

The fundamental goals of a successful building, regardless of location, aesthetics, program, owner, and building type, are essentially to keep water out and allow thermal control within. The building envelope encompasses the entire exterior surface of a building, including walls, doors, and windows, which enclose, or envelop, the interior spaces. Weaknesses in the building envelope can result in several undesirable results, from moisture infiltration, often leading to mold and mildew; damage caused by wind loads, high energy costs, ongoing maintenance problems, and failure of one or more architectural and engineering building systems. Any of these scenarios, and the numerous ripple effects that may ensue, can potentially increase risk and liability concerns for architects, design professionals, building owners, and occupants.

For these reasons, and the desire to promote sound professional design standards, a thorough understanding of building envelope design methods and construction techniques are critical aspects of architectural practice. When building envelope problems arise, liability concerns often focus on factors and parties relating to design, construction, manufacturing, and testing of systems and materials.

Innovative architectural design is enhanced by careful attention to detailing, selection and specification of compatible materials and related component systems. At the same time, architects, specifiers, and design professionals must be aware of component installation methods and construction techniques. With so many advances in manufacturing processes, emerging new materials, and enhanced technology in the marketplace, along with ongoing updates of building codes and industry testing criteria, and an often unskilled labor force, the required knowledge base for effective building envelope design is constantly expanding.

The new Charlotte Bobcats Arena is checkered with insulated metal composite wall panels in custom shades of gray for an original appearance. Photo credit: Centria

"A multi-component building envelope system that is engineered, fabricated, and assembled by the manufacturer can reduce design efforts, errors, and associated liability, if architects and specifiers can define the required performance criteria. Because the system can be tested as an assembly extensively in labs, it avoids field-testing, which is often required for large-scale buildings or critical facilities. The systems also benefit owners of large and multiple facilities because of the standardization of facility design and management. They generally simplify construction planning and shorten project duration," observes Tian Feng, AIA, FCSI, Chief Architect, San Francisco Bay Area Rapid Transit, and former construction expert witness consultant, Oakland, California.

This article will address several components and systems that comprise the building envelope, and explore innovative qualities, trends, and characteristics. These building envelope design elements include: high performance insulated metal composite panels; point supported, bolted glass systems; curtain wall and ribbon window systems; seamless building envelope solutions using different types of glass and fenestration components; hurricane-resistant aluminum composite materials with high strength organic fiber, and a product not visible on the building envelope exterior, a liquid-applied flashing system.

Insulated Metal Composite Panels

Innovative building envelope materials often address several issues, from promoting sustainability and energy efficiency, to minimizing liability and risk stemming from mold issues. At the 2006 AIA Convention, William McDonough, FAIA, described the development of "cradle to cradle" strategies, which analyze the nature of materials in products. This analysis goes beyond cradle to grave (manufacture to disposal), extending from creation to re-creation, through complete cyclical reuse.

Sustainability and Product Life Cycle

Cradle to Cradle Certification, a new sustainability evaluation method, is administered by McDonough Braungart Design Chemistry (MBDC), which reviews material or product ingredients, and the formulation for human and environmental health impacts throughout the overall life cycle. The certification assesses a material's potential for being recycled or safely composted. Certification criteria include: material reutilization and design for the environment; energy; water, and social responsibility. The program focuses on products whose materials are perpetually circulated in closed loops, thus cradle to cradle.

In the final phase of a campus transformation, insulated metal composite panels on the exterior of the housing building help create the new focal point of the University of Cincinnati campus. Photo credit: Centria

A series of insulated metal composite panels have met, or exceeded, certification criteria. These insulated metal composite panels have several characteristics that may help a building qualify for credits within the U.S. Green Building Council's Leadership in Energy and Environmental Design (LEED®) Green Building Rating System, including:

• Tested insulation value: Based on independent testing, insulated metal composite panels show low U-values, ranging from 0.050 to 0.076 (lower is better). This series of metal composite panels provides superior insulating value that can result in significant energy savings.
• High recycled content: Based on the LEED®-NC Reference Guide, this panel series has an average post consumer recycled content of 16 to 19 percent, and an average post industrial recycled content of six to seven percent, for a total recycled content of 22 to 26 percent.
• Low-emitting materials: A factory-applied sealant may have a volatile organic compound (VOC) below the limit established by LEED®.
• Reduced jobsite scrap: Pre-fabricated panels made in the factory result in little to no jobsite scrap generated, since field cutting of the panels is generally not required. Products that are shrink-wrapped eliminate wasteful crating and packing materials.
• Regional materials:LEED®-NC (for new commercial construction and major renovation) provides credits for products manufactured within 500 miles of the project site. In many instances, this criteria is achievable for insulated metal composite panels systems.
• Sustainability: Insulated metal composite panels replace multiple materials with one-piece panels, reducing jobsite scrap and minimizing the fuel consumption multiple freight deliveries would require. The durability and advanced thermal and moisture protection qualities of insulated metal composite panels promote energy efficiency and reduce maintenance demands.
• Durability: Insulated metal composite panels are durable, low maintenance, and decrease the need for water-washings or toxic chemical cleanings. A product life cycle averaging 20 years or more minimizes the need for replacement.
• Energy costs: Reflective coatings are typically available for high solar reflectance, potentially resulting in lower building cooling costs.

Thermal and Moisture Protection

Advanced thermal and moisture protection (ATMP) refers to building envelope wall systems that provide superior thermal and moisture control, especially when compared to traditional wall systems.

Innovative ATMP solutions involve insulated metal composite panels that are installed outboard of a building's metal studs. Available systems can be utilized individually as a complete exterior wall system or combined with other exterior aesthetic panels for a superior multi-component wall solution. ATMP is important because many city, state, and national codes are requiring better thermal barriers within the building envelope, as energy conservation continues remain a priority.

Even the smallest leak in an air or vapor barrier can be a potential source for moisture control failure. Air and pressure alone can cause significant amounts of moisture-laden air to flow through cuts, rips, and staple penetrations. The moisture can condense and remain inside the wall cavity, damaging materials, and thus creating an environment for mold, which causes other problems.

Liability Issues

Mold concerns and related health issues linked to this fungus have been the central issue of many lawsuits. The Insurance Information Institute estimates that $3 billion in building mold claims were paid in 2002. Specifying an insulated metal composite panel system engineered for superior thermal performance and moisture control will significantly reduce mold-related risks for owners, occupants, and design professionals.

There is another reason that specifying such systems will further reduce risk and liability. "Insulated metal composite panel construction requires one supplier and installer, so the need for multiple trades, contractors, materials, and manufacturers on the jobsite is significantly reduced. In other types of construction, if leaks occur, it's hard to determine who is responsible for the faulty work or installation. High performance insulated metal composite panels eliminate this potential scenario, thereby reducing risk and liability concerns for owners and architects," said Rick Brow, Director of Marketing, CENTRIA Architectural Systems, Moon Township, Pennsylvania.

Insulated metal composite panels with an aggregate coating create the appearance of pre-cast on the exterior of the Parkwest Medical Center in Knoxville, TN. Photo credit: Centria

Insulated metal composite panel systems are suitable in new construction and renovations, in all climates. In addition to sustainability, superior thermal and moisture protection performance, and reducing mold concerns, they offer aesthetic qualities as well. Insulated metal composite panel systems are available in a variety of finishes, colors, shapes, and profiles with reveals, curves, and other design options that meet technical criteria, testing standards, and national codes.

Point Supported, Bolted Glass: Maximizing Transparency

Building envelope materials and systems can enhance dramatic interior spaces, such as lobbies and public assembly areas, by maximizing natural daylight and visibility to the outdoors. Point supported, bolted glass systems provide maximum transparency to large expanses of the building envelope. This bolted glass system relies on mechanical fasteners to connect the glass to the structural frame, without mullions.

The point supported, bolted glass system is comprised of glass, fittings, and structural supports. Each element has many options, to meet the design solution for various applications. Structural glass façades rely on the quality of the glass for their performance and aesthetics. An extensive range of glass types can be used with this system, for flexibility of design, appearance, performance, and transparency, such as tempered, laminated, coated, insulating, high performance energy efficient, acoustical, and solar glass.

The Mall at Millenia, in Orlando, Florida, uses point supported bolted glass to maximize transparency between the outdoors and the indoor retail environment. Architect: JPRA Architects Photo credit: W&W Glass

Structural elements that work with the system include stainless steel cables, space frames, simple steel pipes and tubes, and elaborate prefabricated trusses. The fitting is critical, to ensure loads are transferred to the structural elements supporting the glass.

Point supported, bolted glass is a flush glass application using a countersunk bolt in the glass that is bolted to the building structural system. This method provides a flush glass surface using countersunk holes, and stainless steel fittings to connect the glass façade to the structure, instead of the conventional framing systems. The result is an engineered system with minimum of structure and maximum visual clarity. A silicone seal between adjacent panels provides weatherproofing.

These systems are suitable for various applications and projects of all sizes and budgets, not only for monumental, iconic buildings. Successful applications include airports, high-rises, cultural facilities, shopping malls, courthouses, universities, hospitals, and corporate headquarters.

Design and Performance Benefits

The point supported, bolted glass system is suitable for new construction and renovation, in any climate zone. Flexibility of design options enables architects to use tinted glass, silkscreen patterns, various colors, as well as large spans of glass. Other advantages include:

• Ability to glaze in any plane, up, over and under, from canopies and roofs to skylights and soffits, without metal framing.
• Enhanced thermal and optical performance, with the use of soft coat Low-E products, to provide better thermal insulation and solar control.
• Acoustical high performance.
• Impact resistance, and tested for various conditions and codes.
• Blast resistance, through the use of specially engineered connections and high-strength laminates.
• Resistance to high winds and seismic loads.
• Design for peak performance properties, including for a super typhoon, equivalent to a Category 5 hurricane in the Far East, for over 200 psf pressure.

This glass system has been tested for hurricane impact in Broward County, Florida. Based on updates to the Florida Building Code, as of Summer 2006, additional test results are pending.

Point supported bolted glass allows visitors to enjoy natural daylight at the Rose Center for Earth & Space, American Museum of Natural History, New York City. Architect: Polshek Partnership LLP Photo credit: W&W Glass

Recent Developments

Bolted glass products have three new and innovative developments, impacting performance and aesthetic qualities.

New technology has allowed the countersunk bolts to be hidden, concealed, or sunk in the glass panel, further eliminating the use of metal. The result enhances the overall look of the glass façade.

Bolted structural glass is fully tempered for strength. New tempering technology is available to create glass that is flatter, and minimize waviness, known as roller wave distortion. During the tempering process, glass softens as it gets hot. Newer tempering furnaces and technology can limit roller wave distortion, thereby improving the optical qualities of tempered glass.

Newer quality control measures and techniques will reduce nickel sulfide, and thereby limit breakage. Nickel sulfide is a contaminant inherent in heavy float glass, which is typically 12mm (about a half-inch) thick, or greater. During the tempering process, contaminants are trapped and can expand, causing spontaneous breakage. The goal during quality control is to limit and catch the nickel sulfide in the glass, and create a safer product through what is known as the heat soaking process.

"These products need complete, fully engineered systems in order for the owner to obtain their full benefit. The glass and related hardware fittings go together, and should ideally be from the same source, not different systems with different warranties, which increases risk to the owner and design professionals," says Jeffrey Haber, Managing Member, W&W Glass, LLC, Nanuet, New York.

To avoid these potential problems, specifications should indicate a single source approach for furnishing and designing the system, to ensure that one manufacturer is responsible for engineering and glass production. This will provide better integration of all system components and warranties, and minimize risk and liability.

As in other building envelope systems, it is important that compatible elements perform to specified loads, meet aesthetic criteria, and don't leak or become maintenance problems over the building and product life cycle, which generally ranges from 20 to 50 years.

Curtain Wall and Ribbon Window Systems

Architectural product manufacturers are increasingly developing systems comprised of compatible components that often provide many advantages. Another approach to this trend involves the use of curtain wall and ribbon window systems, utilizing aluminum fenestration. Curtain walls refer to a system that does not carry any dead load from the building other than its own weight. The loads are generally transferred to the main structure through connections at floors and building columns. Curtain walls are designed to resist air and water infiltration, and span multiple floors. Ribbon windows are horizontal architectural elements that are located around the building façade on a per floor basis.

"Building envelope systems must be designed with the goal of reduced field labor costs, greater thermal efficiency, and more flexibility for off-site assembly, sealing, and glazing. This will result in savings that can be passed on to building owners," says Greg Hall, Senior Product Development Designer, Vistawall Architectural Products, Terrell, Texas.

Curtain wall and window systems with excellent thermal performance can lower energy costs and add natural daylight to public spaces. Photo credit: Vistawall

A new high-performing pressure-equalized curtain wall system features exceptional water control, outstanding thermal performance, straightforward fabrication techniques, and easy installation. Several new related curtain wall framing systems share many common parts, such as gaskets, setting blocks, face members and anchors. This common chassis allows architects to combine two applications, curtain walls and ribbon windows, from a single system on the same building. These compatible parts allow easy transitions to occur between curtain wall and ribbon window details, design features, and construction installation. Use of common members and components between systems reduces construction errors and costs, and simplifies site fabrication.

Among the curtain wall and ribbon window systems, even more variations are available, such as a traditional pressure wall system, composite vertical mullion with traditional pressure wall horizontal members, and inside-glazed curtain wall, utilizing composite mullions throughout. These systems are typically available to meet a range of performance and thermal efficiency criteria. For maximum flexibility, these systems also share a common platform, the same glazing pocket design. This allows easier transitions from one system to another in the same project.

Curtain wall and ribbon window systems offer many component variations to allow design flexibility and thermal efficiency. Photo credit: Vistawall

Curtain wall systems that offer excellent thermal performance can provide lower energy costs to building owners and tenants, and add to a project's sustainability features.

Some new curtain wall systems utilize composite mullions, which offer several advantages. They include better thermal performance, decreased field labor due to factory-assembled one-piece design, and reduced glazing time due to elimination of screw-applied temporary glass retainers.

The inside-glazed version of the composite mullion curtain wall offers added benefits of glazing the system from inside the building. This feature eliminates the need for scaffolding, along with the safety risks and field installation costs, and further improves thermal performance. These curtain wall systems are suitable for projects in all climates, year round.

Flexibility of design options is another aspect that allows design professionals and specifiers to address finishes, sunshade systems, loading capabilities, horizontal mullions, and various tools for LEED® certification under the U.S. Green Building Council's LEED® Green Building Rating System.

A new ribbon window system provides a high level of thermal performance, and offers many accessories to accommodate various door framing and anchoring options. High performance criteria include levels of air infiltration, static water, deflection load, structural load, sound transmission class (STC), thermal performance, and testing results and certifications by recognized industry organizations, such at the National Fenestration Rating Council (NFRC).

Seamless Building Envelope Solutions and Solar Glass

Innovation can apply to the way services are delivered, as well as to new and different methods of using technology, materials, and products. Delivering quality products and services in the building industry is generally dependent on effective project management, and meeting budgets and schedules. When manufacturers meet project targets, they provide enhanced value to building owners and design professionals, in addition to the high performance characteristics inherent in the building envelope products they provide.

Four Seasons Hotel & Tower, Miami, Florida. Architect: Bermello, Ajamil & Partners and Gary Edward Handel Associates. Photo: Courtesy of Oldcastle Glass

Multiple vendors, trades, installers, and contractors can complicate project coordination, especially when glass, metal, and storefront window suppliers and different warranties are involved. Each additional party and company involved during the design, construction, manufacturing and testing process adds more risk to projects, as well as potential costs and scheduling challenges.

"Providing a one-stop, seamless building envelope solution to owners, architects and design professionals can significantly streamline construction management. The benefits of this approach include reducing the number of vendors, better delivery coordination, minimizing procurement delays, and the ability to provide a single warranty for the entire system. All of these factors mean less risk during construction, faster project completion, and lower total project costs," says Deep Bhattacharya, Vice President of Business Development and Technology, Oldcastle Glass, Inc., Santa Monica, California.

Architectural elements considered part of building envelope solutions include curtain wall systems, skylights, operable windows, storefronts, doors, and structural glass walls. Additional elements that are part of the building envelope include glass canopies, metal panels, revolving and sliding doors, and related engineered products.

Energy Efficiency Through Solar Control Glass

With energy costs rising steadily, the need to control solar heat gain and maintain energy efficient buildings that provide occupant comfort and aesthetics is an opportunity for innovation.

A new type of neutral color solar control glass allows sunlight to enter a space, without accumulating heat gain, through a combination of high performance solar control and visible light transmittance. This solar glass can provide significant reductions in energy costs, and heating, ventilation, and air conditioning (HVAC) equipment expense. Solar glass also reduces harmful ultraviolet rays that can discolor fabrics and finishes, causing them to fade, so interior furnishings will look better over time.

Image courtesy: Oldcastle Glass

The Light to Solar Gain (LSG) value of solar glass far outperforms high performance solar control Low-E glass, and clear insulating glass, at values of 2.14, 1.44, and 1.12 respectively. The higher the LSG value, the better the glass performs at transmitting daylight and reducing heat gain from the sun.

These qualities contribute to the sustainability of solar glass, from energy efficiency and maximizing the use of natural daylight to minimizing ultraviolet rays and enhancing occupant comfort.

Hurricane Impact-Resistant Glazing

Glazing has always been vulnerable to the high winds and flying debris that occur during hurricanes. High performance hurricane impact-resistant glass can withstand 140 miles per hour (mph) winds, along with high-speed projectiles and debris, including design pressures in excess of 100 pounds per square foots (psf). These standards are tested and proven by independent laboratory results.

Hurricane impact resistant glazing meets the most stringent building codes for large glazed openings up to 50 sq. ft. in residential and commercial applications. This results in an aesthetic and functional design solution that provides peace of mind for owners and architects.

Capturing the Building Envelope

Many types of engineered glass products can be used on the building envelope to address different owner needs, code requirements, and design challenges. Building envelope applications include the following:

• High performance glass: Attack-resistant laminated glass, bullet-resistant laminated glass, decorative glass, solar control insulating glass units, fire-rated glass, and hurricane-resistant laminated glass
• Blast-resistant windows
• Engineered curtain wall
• Operable windows
• Storefronts and doors
• Structural glass walls
• Additional elements include glass canopies, metal panels, revolving and sliding doors, and skylights

Aluminum Composite Material with High Strength Organic Fiber

After the 2005 hurricane season that devastated parts of the Gulf Coast, the insurance industry is increasingly seeking a high level of protection against major storms. "When New Orleans and the Gulf Coast were severely hit by Hurricanes Katrina and Rita, flying debris caused significant damage, in addition to the flooding that devastated these areas. Some building envelopes and materials held up better than others against the impact of this debris. In some cases, the wind pulled exterior wall materials away at a corner or flying debris hit the building just right to break open a corner, resulting in exterior materials being torn off the building, causing more damage," observes Doug Ashe, AIA, principal, Ashe Broussard Weinzettle Architects, Alexandria, Louisiana.

Withstanding Hurricane Force Winds and Wind-Borne Debris

New products for commercial buildings are engineered to help provide protection from the damage of hurricane wind-borne debris. These durable architectural panel systems are designed to withstand wind-borne debris and wind speeds up to 130 mph, which are common in Category 3 hurricanes.

Combining the weight and flexibility benefits of aluminum materials with the high impact-resistant strength of a synthetic organic fiber widely known for its use in bulletproof vests and body armor creates a safety net by helping to protect building façades from hurricane-propelled debris, frequently the main source of hurricane damage.

The composite panel system consists of a thin layer of this high strength organic fiber material placed between the aluminum skins and polyethylene core. Lightweight and flexible, aluminum composite material with high strength organic fiber can withstand hurricane-propelled debris and similar types of impact.

Exterior building panels of aluminum composite material with high strength organic fiber passed rigorous simulated hurricane impact tests conducted by Hurricane Test Laboratory, LLC in Florida. The tests included the "large missile impact test," involving a nine-pound, two-inch by four-inch timber traveling at 50 feet per second, as required by the Miami-Dade Building Code. As of Summer 2006, official approval of the aluminum composite material with high strength organic fiber is pending from the Miami-Dade County Building Code Compliance Office.

High Strength Organic Fiber Material

This well-known, high strength organic fiber material is often used in high performance security products, such as lifesaving bulletproof vests and body armor for law enforcement, correctional, and military personnel. The material is also used in blast curtains, which are made from strong, tightly woven materials, such as high strength organic fiber, polyester or carbon fiber. Blast curtains are often used inside high-risk buildings considered terrorist targets, to protect building occupants by catching exploding glass shards and debris.

The high strength material consists of organic fibers with long molecular chains that form a strong bond, resulting in several unique properties. General properties such as high tensile strength at low weight, structural rigidity, dimensional stability, high cut resistance, and flame resistance make this material an ideal component when combined with an aluminum composite panel designed to resist the high winds and flying debris typically occurring during hurricanes. In this building industry application, high strength organic fiber material provides superior impact resistance, similar to how it works as a protective barrier around jet turbine blades and luggage containers for aircraft to help shield passengers from flying debris, in the event of an explosion.

Stopped in its tracks: In this lab test, debris hurled with hurricane force fails to break through aluminum composite material with high strength organic fiber. Photo credit: Alcoa

Aluminum composite material with high strength organic fiber is well suited for commercial office and public building façades, especially schools, libraries, museums, hospitals, and other small and mid-sized structures in hurricane prone areas, like the U.S. Gulf region. "Protecting commercial buildings from hurricane damage results in maintaining livelihoods, allowing people to get back to work sooner, generate revenue, and make needed repairs to homes and other structures," says Samuel W. Chastain, Global Director of Marketing, Alcoa Architectural Products. Atlanta, Georgia.

Furthermore, aluminum composite material with high strength organic fiber can be used on the bottom two floors of a structure and matched with standard aluminum composite materials on the upper floors. This is important since Florida building codes require that panel systems in high velocity wind zones provide protection up to 30 feet above the ground. Standard aluminum composite material passes the small wind borne debris test that is required above 30 feet.

Highly Engineered Solution

A lightweight aluminum composite material with high strength organic fiber helps provide protection for a building with a superior strength to weight ratio, that is further enhanced by the extraordinary high strength of the organic fiber material, which is five times stronger than steel on an equal weight basis.

Easy Installation

Typically, panels made of aluminum composite material with high strength organic fiber eliminate the need for protective backer materials, such as plywood and concrete masonry units. Only insulation material is required. Panel modules can generally be shop-fabricated and quickly and easily mounted onto structural steel studs at the jobsite, significantly reducing installation time and labor costs when compared to other traditional materials used on facades, such as brick and stucco.

Generally, initial costs for material and installation of aluminum composite material with high strength organic fiber are compatible with those for traditional materials, but require less maintenance over the lifetime of the product because no repainting is required.

From a design standpoint, aluminum composite material with high strength organic fiber shares the benefits of durability and versatility found in traditional aluminum composite material, which is used in a wide range of interior and exterior architectural and specialty applications. Generally, this aluminum panel system is available in a range of colors, further enhancing architectural aesthetics and design options. Aluminum composite material with high strength organic fiber can be fabricated in angles and curves, offering a flat, smooth, consistent surface; and rolled, routed, and drilled to meet most complex design specifications.

Liquid Applied Flashing System

All of the previous building envelope products discussed are visible exterior building design elements. However, building performance relies on many components that contribute to keeping buildings dry. Flashing is the system that prevents water and moisture from entering a building at wall and window openings and penetrations.

"In many cases, the components you cannot see in a wall assembly serve a more important role in the overall building envelope performance than the components you can see. For architects, the specification of fluid applied flashing and weather resistive barrier products facilitate ease of detailing, interpretation, coordination, application and above all, contribute to the overall long-term performance of a building, leading to piece of mind for both the architect and the building owner," says Robert W. Dazel, AIA, Regional Manager Midwest, Dryvit Systems, Inc., Monroe, Michigan.

Liquid applied flashing systems consist of mesh tape and two coats of fluid at the window rough opening. Upon curing, a chemical bond forms, creating a seamless flashing condition. Photo credit: Dryvit

The liquid component of some flashing systems is an extremely flexible, waterproof, water-based polymer material used in conjunction with a compatible mesh tape, to seal substrates around windows, doors, and other openings. The flashing system provides an effective water-resistant membrane designed for use with certain building envelope systems, and is an acceptable alternative to flashing tape. It can also be applied to bridge across floor lines and other construction joints.

Traditional flashing methods include a peel and stick membrane that must be cut to size, and carefully installed by the general contractor. Design professionals must be able to provide details and specifications so the contractor can install the system under proper temperature conditions. A mechanical bond forms when one piece of peel and stick membrane laps over another and adheres to it.

With a liquid applied flashing system, reinforcing mesh is applied to the window rough opening when the first coating of fluid is still wet. The second coating forms a chemical bond. The fluid applied flashing cures, or sets, into a membrane-like product. When the system cures, it creates a seamless flashing condition, through this chemical bond. The liquid can be applied to most traditional building envelope materials, but not to pressure treated or fire treated plywood, or other treated materials. The cured flashing system has no seams, holes or punctures, often the sources of water infiltration, that may result with the use of peel and stick flashing tape.

Flashing System Benefits

This liquid applied flashing material and mesh system is easy to install, is used directly from the pail, and can be applied using a brush or roller over approved, clean, dry substrates. Drying time depends upon the air temperature, wind conditions, and relative humidity.

Unlike other traditional flashing methods where workmanship and extensive training may be required for proper installations, an unskilled worker can be readily trained to install this system quickly and on-site.

Architects need not develop details for this system at openings and wall penetrations; a single line shown on drawings as flashing is sufficient. This eliminates another potential problem for the architect and the contractor. The system is flexible, appropriate for new construction and renovation, in residential and commercial buildings, in any climate.

Minimizing Liability

Traditional flashing systems depend on proper materials, details, specifications, installation conditions, and workmanship. Failure of any of these elements to perform increases the potential for building envelope moisture intrusion, which can lead to leaks, mold, and potential lawsuits.

Use of a liquid applied flashing system eliminates many of the variables that can lead to failure in traditional flashing systems, thereby minimizing liability and risk. This flashing system works well with overall building performance criteria to keep moisture out of walls and interior areas.

According to Tian Feng, AIA, FCSI, Chief Architect, San Francisco Bay Area Rapid Transit, and former construction expert witness consultant, Oakland, California, architects who fail to provide appropriate specifications and flashing details can pay a high price in court. "When I was a construction expert witness, nearly all building failure cases were related to water or moisture intrusion from building envelopes, and over half of those cases were due to flashing failures. While common perceptions attribute failure to workmanship, the reality has been contrary. Successful flashing relies upon more than good workmanship in installation; it begins early on in product selection and specifications.

"The best practice is to define the water and moisture resisting performance criteria, followed by working with manufacturers and installers to determine the appropriate system, instead of reusing old, often outdated, office master specifications and details. I saw too many flawed "cut and paste" specifications and details that rarely held up in court to the experts during litigation. Every one of these "cut and paste" specifications proved to be costly for the design firms and their insurance companies," Feng observes.

Summary

Successful building envelope design requires more than aesthetic qualities on the outside. Keeping water out, heat or cooled air in, and resisting the impact of wind, blast, heat gain, and seismic forces have become among the many challenges facing architects, design professionals and owners. Many of the most important building envelope design elements, such as performance criteria and building system components, are hidden from view. In an increasingly risk-prone environment, and litigious society, design professionals must have a broad understanding of the many factors that contribute to building envelope design and construction.

As this roundup of innovative products, concepts, and trends has demonstrated, architects have many options when reviewing building envelope products, related components, and systems. Increasingly, these new products and systems offer various features that are designed to enhance performance and potentially reduce risk to architects and owners. Installation, warranties, the nature of the labor force, and product delivery schedules are other considerations that can streamline, or complicate, project schedules and budgets.

As far as building envelope trends, sustainability, moisture intrusion, energy efficiency, solar control, enhanced use of glass, new technology, along with high performance composite materials, products, and systems, are likely to remain important product concepts in the building envelope marketplace. If the present is any indication, these products will be constantly changing and updated, to meet the next challenge, capture the next trend, and provide architects with even more exciting design opportunities.

Barbara A. Nadel, FAIA, principal of Barbara Nadel Architect, in New York City, frequently writes about design and technology. She is the author and editor-in-chief of Building Security: Handbook for Architectural Planning and Design (McGraw-Hill, 2004).