Specifying high-performance curtain wall in educational facilities

by sadia_badhon | April 29, 2020 2:00 pm

by Kevin Haynes

[1]

Today’s educational campuses do more than provide weather-tight enclosures for instruction and study. They must be attractive to recruit students, faculty, and donors, and offer both generalized, multipurpose and specialized, purpose-built facilities. These buildings are also expected to be more than functional, comfortable, environmentally responsible, safe, and affordable to maintain.

Modern, aluminum-framed curtain wall systems can meet all of these expectations and performance requirements, as well as construction budgets and schedules. A classroom building will have different design goals than a research laboratory, library, athletic facility, or a student residence hall. A college in Florida will have different code requirements than a university in Washington. While the specification and selection criteria will vary from project to project, curtain wall systems are versatile and dependable in accommodating almost any application on campus.

Common terms and components

A curtain wall system is one of several fenestration products that can be specified to fill an opening. Windows, operable vents, storefronts, skylights, sloped glazing, louvers, and entrance systems may also be used as alternatives, depending on the application, or in conjunction with, curtain wall.

[2]

It can be confusing to understand when to specify storefront and when curtain wall is the better solution. Generally, the answer is based on the height of the openings and the complexity of the project. Like its retail origin would suggest, storefront systems provide an economical fenestration product that can be installed in smaller opening sizes for the ground level through third floors. Curtain wall systems, draped in front of a building’s floor slabs like a curtain, are considered non-loadbearing walls, can span multiple floors, and have a robust range of design and performance options. Curtain wall can also be configured as a fully captured system, or as a two- or four-sided structural glazed system.

The North American Fenestration Standard/Specification for windows, doors, and skylights (NAFS) by the American Architectural Manufacturers Association (AAMA), Canadian Standards Association (CSA), and the Window & Door Manufacturers Association (WDMA) describes:

Curtain wall systems can be factory-glazed or designed to accommodate field fabrication and glazing, including optional structural glazing. Curtain wall typically employs deep rectilinear framing profiles (approximately 150 mm [6 in.] or greater), which are often made available in ‘stock lengths.’ Curtain wall vertical framing members run past the face of floor slabs, and provision for anchorage is typically made at vertical framing members only.

…curtain wall systems often need to meet additional performance requirements for inter-story differential movement, seismic drift, static, dynamic water infiltration, etc.

…curtain walls are not to be confused with storefronts or window walls.

Along with NAFS, industry-leading curtain wall specification guidelines include AAMA CWM-19, Curtain Wall Manual, and AAMA 501-15, Methods of Test for Exterior Wall. These describe the test procedures to validate curtain walls systems’ performance for structural design and overloads, air infiltration and exfiltration, static and dynamic water infiltration, vertical interstory movement, elastic and inelastic seismic movements, acoustics, and thermal cycling.

Standard curtain wall systems furnished in stock lengths tend to be the most economical type. It is also known as the ‘pressure wall’ because it utilizes a deep back member (mullion) available in various sizes from 100 to 200 mm (4 to 8 in.), and a pressure plate assembly to provide compression on the glass for increased performance. Aluminum covers, referred to as ‘face caps,’ conceal the curtain wall systems’ pressure plates and can be specified in angled or rectilinear profiles, and in a range of sizes and configurations, thereby providing a decorative appearance.

[3]

Beyond appearances, curtain wall, storefront, and other fenestration products offer building occupants with natural light, views, and a connection between indoor and outdoor spaces. Operable vents, windows, and doors also enhance natural ventilation. When these attributes are paired with thermal performance considerations, fenestration systems  can contribute to the building’s energy efficiency, resiliency, and cost savings, as well as occupant comfort, productivity, and well-being.

The majority of fenestration systems in commercial and institutional construction, including educational buildings, rely on extruded aluminum for the framing material. The advantages of aluminum include:

• high strength to weight ratio;
• fabrication and design flexibility to create almost any size, and straight and curved shapes;
• infinite recyclability;
• wide range of finish options;
• excellent weatherability properties;
• superior structural performance; and
• engineering potential to meet thermal performance,
  blast mitigation, and hurricane impact resistant criteria.

Code-compliant high performance

The Advance Energy Design Guides (AEDGs) offer recommendations that are aimed at establishing net-zero energy and up to 50 percent energy savings over the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) 90.1-2004, Energy Standard For Buildings Except Low-Rise Residential Buildings, minimum levels. AEDGs recommend “Maximize the use of daylighting and controls through side-lighting and top-lighting strategies in spaces that do not have air change requirements. Design a daylighted school. If carefully designed, vertical fenestration and skylights can help provide interior illumination without excessive solar heat gain. Electric lighting systems can be extinguished or dimmed, saving significant energy and maintenance costs,” (The Advance Energy Design Guides [AEDGs] represent a partnership between the American Society of Heating, Refrigeration and Air Conditioning Engineers [ASHRAE], the U.S. Green Building Council [USGBC], the Illuminating Engineering Society [IES], the U.S. Department of Energy [DOE], and the American Institute of Architects [AIA]).

Key benefits of educational facilities achieving healthy, high-performance learning environments may include:

• increased student cognition;
• fewer absences;
• reduced energy use and associated emissions and natural resource consumption;
• minimized maintenance costs, and associated material and labor costs;
• lower overall operating and life-cycle costs; and
• improved recognition for sound fiscal management.

UNIVERSITY OF NORTH DAKOTA’S ROBIN HALL

The University of North Dakota’s (UND’S) Robin Hall is the headquarters of the unmanned aircraft systems programs at the university’s nationally acclaimed John D. Odegard School of Aerospace Sciences. The building’s sleek, light-filled design features curtain wall and storefront systems to meet the structure’s modern aesthetics, sustainability goals, and performance requirements. The $22-million, 6689-m2 (72,000-sf) aerospace research facility was designed by Icon Architectural Group. As the tallest building in the Grand Forks area, Robin Hall’s base rises five stories, and ascends into a 39-m (127-ft) glass and metal tower at the structure’s entrance serving as a beacon for the entire UND campus. Nearly 929 m2 (10,000 sf) of screw-spline, shear-block curtain wall enclose the tower and lower levels. An additional 130 m2 (1400 sf) of shear-block curtain wall was installed on the northwest corner. Screw-applied pressure bars secure the glass and a cover plate conceals the fasteners. Enhancing the tower’s structural performance, 7938 kg (17,500 lb) of steel reinforce the aluminum curtain wall framing members. For added durability, the aluminum is finished in black anodize. Where curtain wall is not used, 1208 m2 (13,000 sf) of storefront frames the low-rise openings and 33 m2 (360 sf) of interior framing create the vestibule. In total, the aluminum-framed exterior system was fabricated using 1046 m2 (11,261 sf) of ultra-clear, high-performance insulated glass with low-emissivity (low-e) coatings. When backlit at night, it radiates across the campus. During the day time, the interior is brightly illuminated with natural light. Some unusually shaped, trapezoidal units were necessary to achieve the precise appearance of the tower and the lower concave, segmented wall. These units were pre-glazed in the glazing contractor’s facility and then shipped to the jobsite for installation. This reduced the time to install that portion of the building and sheltered other work during the winter construction schedule. Inside Robin Hall, four floors house a large auditorium, study space, administration offices, classrooms, collaborative learning spaces, and a hangar space for flight testing. The building’s basement also includes an open research space with laboratories and simulators. A skywalk directly connects the facility with two other UND aerospace buildings.

KAISER PERMANENTE SAN DIEGO MEDICAL CENTER

[4] East Carolina University’s (ECU’s) 2019 home football season ushered in the beginning of a new era for Pirates fans at Dowdy-Ficklen Stadium. The $60-million renovation added 1000 seats on the south side of the TowneBank Tower. Designed by architectural firm LS3P Associates of Wilmington, North Carolina, the Dowdy-Ficklen Stadium south side renovation project team also involved AECOM. LS3P specified the curtain wall, storefront, ribbon windows, and entrance systems. These aluminum-framed fenestration products were installed on the public façade, and on the interior glazing systems. According to the glazing contractor, it was a challenging project from the early stages. The system needed to load structurally and withstand the stacking pressures at the top/press level of the tower on the field side. The curtain wall manufacturer pre-engineered an inside glazed system to meet the project’s performance requirements, construction schedule, and budget. With respect to future building maintenance, the exterior curtain wall, windows, and entrance systems were finished in a Class I clear anodize. Ideal for high-performance, weather-exposed building products, this finish presents a contemporary appearance that can withstand the heavy traffic of excited football fans and the extreme coastal weather that can hit ECU’s campus. Anodized aluminum resists the ravages of time, temperature, corrosion, humidity, warping, abrasions, and wear. An integral part of the substrate, the anodize finish protects the structural integrity of the aluminum, adding to its long life cycle. On the interior, framing systems provide views from the TowneBank Tower to the field, as well as transparency and separation between the premium suites, loge and press level, and the main concourses. These storefront systems used a 70 percent polyvinylidene fluoride (PVDF) resin-based architectural coating in a light beige color. These coatings exhibit outstanding resistance to humidity, color change, chalking, gloss loss, and chemicals to ensure a long-lasting, durable finish that protects the aluminum, contributes to its low-maintenance longevity, and meets the desired appearance. The original stadium opened in 1963 and consisted of the permanent stands on the south side and a small press box. The last significant construction project at Dowdy-Ficklen Stadium was the 2010 completion of a 7000-seat expansion in the east-end that increased capacity to approximately 50,000. The 8640-m2 (93,000-sf) TowneBank Tower rises nine stories and spans the top of the south-side seats between the 14-m (15-yard) lines. The top level of the tower also houses a new press box and game-day operations center. Along with the TowneBank Tower, renovation of the Wards Sports Medicine Building was also part of the project scope. Expansions and modernizations were made to the Ward building’s football locker room, team meeting areas, athletics training headquarters, and equipment room. A football team lounge also was added to the existing structure. Praised as a state-of-the-art, first-class facility and a community asset, the new stadium also intended to assist with the university’s recruitment of college athletes. Demonstrating this success, ECU has already signed 25 new players for the 2020 season.

DAN DIPERT CAREER AND TECHNICAL CENTER IN TEXAS

[5] The Dan Dipert Career + Technical Center (CTC) serves approximately 2400 high school juniors and seniors from across the Arlington Independent School District in Texas. Designed by VLK Architects, CTC emphasizes transparency to promote collaboration and connection. Incorporating curtain wall, storefront, entrances, diagonal sun shades, and interior framing systems, CTC’s purpose-built, two-story structure spans 15,775 m2 (169,800 sf). The facility is designed for flexibility to evolve and adapt to changing programs and future areas of interests. According to the architect, the school also serves as a subconscious billboard to the community, visitors, and students who understand they are entering an institution of higher learning and not just another run-of-the-mill high school building. Distinguishing itself, the CTC’s custom 610-mm (24-in.) vertical sun shade detail runs the length of the 230-mm (9-in.) deep curtain wall. Not only is the sun shade custom, but it is also on a slant connecting at the bottom of one vertical curtain wall mull and carries across to the top of the next one. A 3D printer was used to create various sizes and thicknesses of the sun shade detail. These prototypes saved money and time, and assisted the architect in determining the right look before committing to the expense of new dies. Enhancing the façade’s strength and thermal performance for the Texas heat, CTC’s storefront and curtain wall systems both use high-performance, low-emissivity (low-e) glass. This helps block unwanted solar heat and allow in visible light for year-round comfort, as well as heating and cooling cost savings. Further minimizing costs and maintenance, the clear anodize finish on all of the 22,860 m (75,000 ft) of extruded aluminum framing protects the structural integrity of the metal for lasting durability. Inspired by the building itself, VLK Architects also designed CTC’s brand image with a repeating pattern reminiscent of the sun shade fins. Inside CTC, this pattern reoccurs in wayfinding and signage, and the interior flush glaze framing system maximizes transparency and daylighting.

[6]

Thermal and condensation performance

To achieve the intended energy goals and improve occupant comfort of an educational facility, the curtain wall’s aluminum framing members must be physically separated to reduce thermal bridging and conduction. Heat loss is transferred through a window by four mechanisms—conduction, convection, radiation, and air leakage. U-factor measures the rate of heat transfer and indicates how well the window insulates, generally in a range between 0.20 and 1.25. With this measurement, a lower U-factor indicates better performance and less transmittance.

In aluminum curtain wall framing, the reduced transmittance is accomplished with a thermal isolator, a low conductive material that separates the pressure plate and back member. To improve energy performance and lower the U-factor, an additional second thermal barrier is created by utilizing thermal struts (insulating strips) within the back member.

Thermal isolators for various climate zones are as follows:

• equal to or greater than 1.6 mm (63 mils), but less than 5.3 mm (209 mils) is used in ‘thermally improved’ systems sufficient for warm-humid Climate Zones 1 to 3;
• greater than 5.3 mm is used in ‘thermally broken’ systems typically sufficient for mixed Climate Zones 4 to 6;
• combining a thermal isolator with polyamide thermal struts, or with a poured-and-debridged barrier, creates a double thermal break to further enhance performance;
• a double thermal break with a larger strut or with dual poured-and-debridged barriers, allows for triple insulating glass, offering an even more effective barrier in very cold climates, and these systems can be used up to Climate Zones 7 to 8 when utilized with appropriate glass; and
• pressure plates made from alternate materials, such as glass-reinforced polyurethane, polyamide, and fiberglass can be employed in the above combinations to enhance the curtain wall’s thermal performance.

Along with providing a comfortable, consistent, year-round interior temperature, a thermally broken, high-performance curtain wall can play a critical role in promoting safer and more resilient buildings. The thermally broken, metal framing also helps control condensation that otherwise could promote the growth of mold, mildew, and microorganisms, which can harm the health of building occupants.

Hazard mitigation

The I-codes are intended to benefit local communities through adoption in accordance with the laws and procedures of a governmental jurisdiction. When adopting a model code, some jurisdictions amend the code in the process to reflect local practices and laws.

For example, the Florida Building Code (FBC) has more stringent guidelines for high velocity hurricane zones (HVHZ) required in south Florida’s Dade and Broward counties. A National Institute of Building Sciences (NIBS) research study reported hurricane wind mitigation in new buildings has a benefit-cost ratio of 5:1 with every $0.72 invested yielding a $3.80 benefit.

The American Society of Civil Engineers/Structural Engineering Institute (ASCE/SEI) 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, describes the means for determining design loads including dead, live, soil, flood, tsunami, snow, rain, atmospheric ice, earthquake, and fire, as well as how to assess multi-hazard load combinations. The NIBS research study estimated implementation of recommended I-code mitigation strategies could “prevent 600 deaths, 1 million nonfatal injuries, and 4000 cases of post-traumatic stress disorders (PTSDs) in the long term.”

High-performance curtain wall systems can not only help protect people and property from natural disasters, but can also mitigate manmade risks such as forced entry or blast hazards. Often, curtain wall systems engineered for hurricane and blast mitigation must be specified with reinforced steel to avoid excessive deflection and rotation. When specifying protective curtain wall systems for blast, hurricane, forced entry, and human impact, it is important to ensure the appropriate glass and glazing method are clearly identified in appropriate specification sections.

Manufacturing and installation

The curtain wall’s extruded aluminum, finished framing members, and glass can be installed and glazed in the field or pre-assembled in sections. In some instances, they can be pre-glazed in the manufacturing facility or by the glazing contractor. Curtain wall framing members are often assembled using either shear-block or screw-spline construction.

Shear-block assembly

The shear-block assembly method for curtain wall framing members involves connecting the horizontal member to the vertical member using an aluminum shear block with integral screw-splines and as well as non-exposed fasteners. Starting from one side of the opening, the vertical mullion or vertical jamb is installed and the corresponding horizontal members are attached to the vertical. Then, the next vertical is attached to the horizontals in a stick-by-stick method.

[7]

Screw-spline assembly

The screw-spline assembly method utilizes integral splines within the horizontal extrusions. This eliminates the need for shear blocks. Vertical mullions are two-piece interlocking extrusions. Horizontals are attached to the verticals using a screw through the vertical into the screw-spline in the horizontals to form pre-assembled ladders in the shop or field.

Water management

Each lite of glass within the curtain wall is sealed, thereby creating individual zones to manage water infiltration. Water entering the framing system is contained within the glass pocket at the bottom of each glass lite and drained to the exterior through weep holes. These holes are positioned in the upper portion of the pressure plate, and at the bottom leg of the face cap, or ends of the covers.

In equalized pressure conditions, the exterior glass and aluminum faces act as a rainscreen, diverting water. The interior glass face and aluminum glazing pocket are connected by gaskets, which act as an air barrier. Water entering the glazing pocket exits via the weep system.

To minimize infiltration issues, the air barrier system should be tied to the curtain wall and other fenestration products. These systems should be installed prior to insulation and façade cladding.

Depending on the project’s size and schedule constraints, the glazing contractor may prepare the curtain wall in its own facility and then ship the units to the jobsite, or it may have the materials sent directly to the jobsite in sequential phases for onsite installation. It is essential to coordinate the curtain wall installation in conjunction with all other building trades.

Customization and compatibility

Standard curtain wall systems can be customized by incorporating a variety of glazing and infill panels, integrating other solar control and fenestration products, and finishing the framing in unique hues and school colors.

Glass

The curtain wall’s design needs to account for the glass width. This may extend from 6 mm (¹/₄ in.) to triple-thick glazing. Generally, an insulating glass unit (IGU) measures 25 to 44 mm (1 to 1.75 in.).

Glass types should be considered separately for each orientation of the building, and when it is possible, with respect to each room’s unique function. As examples, a classroom’s viewing areas would commonly be located at eye level, a laboratory may prefer daylight-only areas where all the fenestration products are closer to the ceiling to avoid glare on instruments and monitors, or a library’s south-facing elevations may require higher performance glass to block more of the direct ultraviolet (UV) radiation and solar heat gain.

Glass selection can be fine-tuned to views, daylight, energy-savings, and comfort by balancing visible light and sound transmission along with managing unwanted solar heat gain, thermal transmission, and condensation resistance. For high-performance and specialty glazing options, additional choices include hurricane-impact resistance, ballistic, blast hazard mitigation, anti-eavesdropping, electrochromics, photovoltaics (PV), and bird-friendliness.

Infill and integrated components

Glass is the most popular infill for curtain wall systems, but not the only option. These aluminum-framed systems can also incorporate metal composite panels (MCPs), masonry, or louvers. In addition to different infill material, curtain wall also integrates and connects with other fenestration products.

Storefront

On multi-story buildings, economical storefront systems are installed on the ground level. It can also be installed in limited applications up to the third floor.

Ribbon window

Typically installed between the floor slabs, ribbon window products are used in ‘punched’ openings, or as a connected ‘ribbon’ of horizontal windows.

[8]

Operable vents

Incorporated within a curtain wall and storefront, operable vents provide natural ventilation or emergency egress.

Doors and entrance systems

Exterior entrances are located at the ground level and installed within a building’s storefront, curtain wall, or façade system. They can also be placed as secured entrances from parking garages or from pedestrian bridges. On upper levels, terrace and balcony doors are also compatible with the curtain wall. It is important to note a subframe is required between the curtain wall frame and door for hinging and locking hardware. Thermally broken entrance systems are available for projects requiring higher thermal performance.

Sun shades

Sun shades are most effective as horizontal overhangs on south-facing elevations when integrated within the overall curtain wall design. With proper site orientation and solar analysis, vertical fins and airfoils also can be added to a curtain wall to provide shading. Both vertical and horizontal shading devices present a distinctive aesthetic that is increasingly seen on campuses across
the country.

Light shelves

Light shelves can be integrated and installed with a curtain wall or other fenestration systems to help reflect and redirect daylight more deeply into a building’s interior.

Other interior applications

Extending natural light and emphasizing transparency, curtain wall, storefront, window, and door systems can also be installed as part of an interior design scheme. Framing and glazing choices may also be specified with upgraded privacy and security features.

Finish and maintenance

Protecting the curtain wall’s aluminum framing, a durable finish also provides a lasting impression. Liquid and powder architectural coatings allow for the greatest breadth with an unlimited spectrum of colors, metallics, or patterns including those mimicking marble, terra cotta, and wood. Anodize provides a more limited color range and the most durable finishes.

Few curtain wall manufacturers can not only custom match a color, but also accommodate separate finish types and tones on the exterior and interior surfaces. When this is available, baked enamel coatings may provide an economical alternative for the interior.

While a rainbow of options are available, white painted finishes and clear anodize remain the popular choices.

Educational facility managers and owners appreciate the minimal effort needed to maintain finished, aluminum-framed curtain wall systems. Clean water applied with moderate and, if necessary, a mild soap is usually all that is required to keep the system looking its best year after year.

[9]Kevin Haynes is an architectural representative for Tubelite Inc. He has more than 25 years of experience in providing technical support to design and specification professionals seeking curtain wall, storefront, entrances, and other aluminum-framed glazing systems for commercial buildings. He has presented continuing education courses on product selection, hurricane-impact resistance, blast hazards, energy savings, and condensation to CSI chapters and members, and to many others in the building envelope community. He can be reached at khaynes@tubeliteinc.com[10].

Source URL: https://www.constructionspecifier.com/specifying-high-performance-curtain-wall-in-educational-facilities/

---