Photo courtesy of NGA; TGP

The right fenestration system can greatly enhance the aesthetics of a project while also providing ample protection from the elements.

Fenestration systems for commercial buildings come in a wide range of types, styles, installation methods, budgets, and performance attributes. The variety available can pose a challenge to architects trying to keep up with the distinctions, advantages, and requirements of different systems. This article will provide a comprehensive overview of storefront, window wall, and curtain wall fenestration systems for commercial buildings. Each style has a very specific application and installation method, and appreciating the distinction between each is critical to ensure buildings are both aesthetically beautiful and help protect occupants from invasive air and water infiltration.

FENESTRATION SYSTEMS FOR COMMERCIAL BUILDINGS

Fenestration systems for commercial buildings encompass a wide range of types, styles, installation methods, budgets, and performance attributes. The variety available in the market poses a significant challenge to architects and builders, who must stay updated on the distinctions, advantages, and requirements of different fenestration systems. This article aims to provide a comprehensive overview of three primary fenestration systems used in commercial buildings: storefront, window wall, and curtain wall systems. Each system has specific applications and installation methods, and understanding these distinctions is vital for ensuring that buildings are both aesthetically pleasing to the public, and well-protected against air and water infiltration to safeguard the structure.

Photo courtesy of NGA

Storefront glazing systems are a favorite for the ground floor of commercial buildings, especially retail shops that want ample light and inviting interiors.

STOREFRONT SYSTEMS

A storefront glazing system is a fixed glazing system that is most commonly used on the ground floor of commercial buildings. They are designed to offer large, clear views, thereby enhancing visibility, letting ample natural light into the building, and providing inviting views to potential customers and passersby. These systems typically span one to two stories and are non-load-bearing, relying on the building structure for support. Storefronts are usually constructed from glass and aluminum frames, providing a modern and sleek appearance.

Storefront glazing systems accommodate glazing infills from ¼ inch to 1 inch in most applications and have profiles that closely mimic typical wall stud framing. The frames are anchored between the floor slabs, and the glass panels are installed within these frames. This method allows for quick and easy assembly, making it a popular choice for retail applications where time and budget constraints are required.

This fenestration is a basic, economical glazing system, often specified where minimum water and structural performance is required. The application of this design is primarily on visibility and accessibility. While they offer adequate protection against air and water infiltration, their performance in terms of thermal insulation and acoustic control is generally lower compared to more advanced systems like curtain walls. However, advancements in glazing technology have improved the thermal performance of storefront systems, making them more energy-efficient.

Many factors determine the proper application of a storefront glazing system. Among them are structural requirements, thermal performance, assembly method, water management, and glazing method.

History of Storefront Glazing Systems

Early storefront systems were composed of wood mullions with an applied sash to hold the glazing in place. As aluminum extrusions became more popular, these systems evolved into tubular framing members with screw applied stops on either side of the glazing infill. Older storefront systems used neoprene plug- or laced-in gaskets on one side of the glass with a wedge gasket on the other, which was placed once the glass was installed. The generic wedge-shaped profile, when installed, creates pressure that seats the glass against the other softer gasket, creating the line to stop air and water penetration.

Modern storefront evolved into a glazing system with integrated glass stops to give a “flush glazed” appearance, thus giving storefront the common name of “flush glazing.” Newer designs incorporate wedge-type gaskets used on both sides to facilitate ease of glazing and reduce the number of required parts. Modern storefront systems, unlike their predecessors, also have systems in place to control water infiltration and the means to evacuate moisture to the exterior.

Performance Requirements of Storefront Glazing Systems

Storefront glazing systems are evaluated and defined by a series of performance specifications from three organizations, the American Society for Testing and Materials (ASTM), the American Architectural Manufacturers Association (AAMA), and the National Fenestration Rating Council (NFRC).

The standards provided by these organizations provide a baseline evaluation methodology to ensure the fenestration system’s reliability, efficiency, and safety.

The primary standards used to assess storefront glazing systems include:

• ASTM E283 (air infiltration)
• ASTM E330 (structural testing)
• ASTM E331 (static water infiltration)
• AAMA 1503 (U-factor and Condensation Resistance Factor testing)
• NFRC 100 (U-factor)
• NFRC 200 (Solar Heat Gain Coefficient and Visible Transmittance)
• NFRC 500 (Condensation Resistance)

Testing for these standards is done in a controlled laboratory environment, and results are then provided to the manufacturers. It is important that architects have a strong working knowledge of the performance attributes of the glazing system to ensure the design, installation, and performance of the glazing system meets or exceeds both performance expectations and local building code requirements.

ASTM E283 - Air Infiltration: ASTM E283 measures the rate of air leakage through a storefront glazing system under specified pressure differences. This test is crucial for evaluating the airtightness of the system, which directly impacts energy efficiency and indoor air quality. By minimizing air infiltration, storefront systems help reduce heating and cooling loads, leading to lower energy consumption and improved thermal comfort. Additionally, a tight seal prevents the ingress of outdoor pollutants and allergens, enhancing the overall indoor environment and creating improved indoor air quality for occupants. The storefront system is subjected to a pressure differential, and the amount of air passing through the system is measured. The results are expressed in terms of air leakage rate, typically in cubic feet per minute per square foot (cfm/ft²) of the storefront area.

ASTM E330 - Structural Testing: ASTM E330 assesses the structural performance of storefront glazing systems under wind load conditions. This test applies both positive and negative pressures to the system to simulate wind forces that the building might encounter. The structural integrity of the storefront is evaluated to ensure it can resist these forces without experiencing excessive deflection, deformation, or failure. Storefront glazing systems are non-load bearing but must be designed and installed to properly support the glass and resist all applied loads, including wind pressure.

ASTM E331 - Static Water Infiltration: ASTM E331 evaluates the resistance of storefront glazing systems to water penetration under static pressure conditions. In this test, water is sprayed on the storefront at a uniform pressure to determine its ability to prevent water infiltration during typical rain events. Controlling water infiltration is vital for protecting the building’s interior from water damage and maintaining a dry and comfortable environment.

It is common practice to apply storefront glazing systems on the first floor of buildings. They are often set back from the most exterior plane of the roofing system to protect the storefront system from direct exposure to rain. These glazing systems are also often used in the first few floors of a building where water and structural performance are not as demanding as that which may be required on a high-rise, multi-span curtain wall system. Because of these constraints, storefront glazing systems need only meet static water infiltration requirements of 8 to 10 psf.

AAMA 1503 - U-Factor and Condensation Resistance Factor (CRF) Testing: AAMA 1503 evaluates the thermal performance of storefront glazing systems by measuring the U-factor and Condensation Resistance Factor (CRF). The U-factor indicates the rate of heat transfer through the storefront, with lower values representing better thermal insulation. CRF assesses the system’s ability to resist condensation formation on interior surfaces. Due to the shorter overall system depths of storefront glazing systems, U-factor and CRF performance will be generally less than that of deeper curtain wall systems.

As the focus on energy efficiency and thermal performance has increased over the past decade, new storefront systems are being designed with superior thermal performance and the incorporation of dual pour and de-bridge pockets, mechanically crimped thermal isolating struts, and in some cases the use of composite framing materials.

NFRC 100 - U-Factor: Similar to AAMA 1503, NFRC 100 involves measuring heat transfer through the storefront, and the results help determine the energy efficiency of the storefront system. NFRC 100 provides a standardized method for measuring the U-factor of storefront glazing systems, ensuring consistent and accurate thermal performance evaluations. Adherence to this standard is essential for energy codes and certification programs.

NFRC 200 - Solar Heat Gain Coefficient (SHGC) and Visible Transmittance (VT): NFRC 200 evaluates the Solar Heat Gain Coefficient (SHGC) and Visible Transmittance (VT) of storefront glazing systems. SHGC measures the amount of solar radiation transmitted through the storefront, which affects the cooling load and energy consumption. VT measures the amount of visible light transmitted, impacting daylighting and occupant comfort. Lower SHGC values are desirable for reducing cooling requirements, meaning the glazing performs better at blocking heat gain. By contrast, higher VT values indicate better natural lighting within the building.

Depending on the type of building and needs of occupants, specifying VT can provide a creative option to satisfy occupant requirements. When needed, lower VT ratings are better suited to reduce natural lighting to avoid glare, provide privacy, or create a specific aesthetic for the interior. For instance, spas, salons, and some restaurants may prefer less natural light.

NFRC 500 - Condensation Resistance: NFRC 500 assesses the condensation resistance of storefront glazing systems, ensuring they can maintain a dry and comfortable indoor environment. This standard evaluates the system’s ability to prevent moisture accumulation on interior surfaces, which is important for preserving indoor air quality and protecting building materials.

Structural Considerations for Storefront Glazing Systems

In some locations, storefront glazing must meet impact resistance requirements, such as those for hurricane-prone areas. This often involves the use of laminated glass and robust framing systems. Likewise, in earthquake-prone areas, storefront systems need to accommodate seismic forces. This may involve additional reinforcement and connections that allow for movement without compromising the integrity of the glazing.

Deflection criteria are specified to prevent excessive movement of the glazing system under load, which can affect performance and appearance. Typically, deflection limits are set to ensure the glazing does not displace excessively, which could cause sealant failure or glass breakage. Also, the design must account for the expansion and contraction of materials due to temperature changes. This can affect the framing and sealants, leading to potential issues with seal integrity and glazing stress.