Glass and Metals 101

An Introductory Guide to Glazing for Architects and Specifiers
Katy Devlin
April 24, 2016
COMMERCIAL, RETAIL, FABRICATION : INDUSTRY TOPICS

Editor's note: The six-part series “All About Glass and Metal: A Guide to Glazing for Architects and Specifiers” began in 2010, with the first installment of “Glass and Metals 101.” This article will update and replace the original “Glass and Metals 101” in the complete series. The full guide also contains insights on topics including glazing specifications, interior glass, protective glazing, building orientation and complex facades. Purchase the guide in its entirety.

"Glass & Metals 101," the 2016 edition of “All About Glass and Metal: A Guide to Glazing for Architects and Specifiers,” returns to the basics, offering an introduction to the glass and glazing industry for architectural students and new design professionals. Additionally, the guide provides insights into trends and recent developments in the glass façade industry for veteran designers and specifiers.

This guide is divided into three parts and presents definitions and descriptions of glass and glazing systems and components, a look at energy performance and daylighting considerations for glazing systems, and answers to common frequently asked questions from architects and specifiers about glass and glazing. But first, the trends.



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Project Overview
Cecil College

The new three-story, 28,683-squarefoot, engineering and mathematics facility at Maryland’s Cecil College features a combination of glazing systems and sun control devices, designed to maximize daylighting and views, while providing thermal efficiency. Natural light is maximized throughout the building and controlled through a central system including daylighting controls, which reduce artificial light levels when available natural light provides sufficient illumination. The architect was Marshall Craft Associates; the general contractor, Riparius Construction Inc.; and the contract glazier, Chesapeake Glazing.

The building features 12,800 square feet of SuperWall curtain wall and 168 linear feet of ClearStory sun shades, from Wausau Window and Wall Systems. Tubelite Inc. supplied 6-by-7-foot double doors and two 3-by-7-foot single doors that flank the building. Linetec finished the aluminum doors, curtain wall framing and sun shades using a two-coat, mica coating in Silver, custom-blended in Linetec’s in-house laboratory. The exterior glass façade uses PPG Industries' Solarban 70XL in 1-inch insulating glass units. Select areas of the glass façade incorporate a custom frit pattern fabricated by Tecnoglass. Additionally, the project exterior is highlighted with large sunshades at the top of the band, and a trellis, which is a main feature of the two entrances, supplied by Americlad, americlad. com. The company also supplied stainless steel column covers, metal wall panels and the coping system.

The glass and metals industry has experienced notable shifts in the last decade, responding to rising performance expectations and growing complexity of façade design. The market has witnessed rapid expansion of product options, as manufacturers and fabricators work to meet demand for better performing glasses, larger sizes, decreased sightlines and decorative options, to name a few leading trends.

“Expectations for glass performance, aesthetics and functionality have been on a constant upward trajectory for the past 10 years,” says Steve Fronek, vice president of technical services for Wausau Window and Wall Systems. “High value added is the rule, rather than the exception, for architectural insulating glass, whether it’s protective glazing using laminated products or polycarbonates; acoustical, laminated glass; spectrally selective, triple-silver, low-emissivity coatings on low-iron substrates; silk-screened or digitally printed patterns; or even dynamic electrochromic glass.”

Driving this value-added trend, particularly for high-performance products, are increasingly stringent performance requirements. “The demand for more high-performance coated glass comes from higher energy costs, greater user awareness of the tremendous energy savings benefits of low-E glass and energy codes such as ASHRAE 90.1-2013 and the 2015 International Energy Conservation Code,” says Brian Schulz, commercial product manager for Guardian Industries Corp. “In addition, there are ‘green’ codes like ASHRAE 189.1 that drive increased use of higher performing glass products. The use of the latest coated glass products are also spurred by LEED certification, mostly for commercial structures. Other factors including shorter lead times and increased quality with consistency and reliability drive change.”

The performance demands have led to improvements in framing systems as well. “LEED as a whole is seen as a big change amongst the construction industry in general,” says Steve Schohan, marketing and communications manager, YKK AP America. “Lower U-factors in the building codes are driving thermally broken systems and high-performance glazing.”

The glass industry has also seen a rise in high-performance products that meet safety requirements. “With an increase in natural disasters and human related dangers, occupant protection has been a hot topic, with more stringent blast specifications, and increased desire for hurricane/impact-resistance products and high-energy performance in the coastal regions,” Schohan says.

Beyond energy performance trends, the glass industry has witnessed extraordinary growth in factory-assembled systems that reduce installation time and cost. “We’ve seen an increase in pre-glazing, shop glazing and unitization,” Schohan says.

Sources also report an increase in complexity, due to rapid advancements in computer modeling tools. “Building Information Modeling and three-dimensional computer design tools have freed design architects from the constraints of rectilinear geometry,” Fronek says. “Many high-end projects start the engineering process as 3D models, and stay in 3D through fabrication and installation. Rapid prototyping, also called 3D printing or stereo lithography, is used by manufacturers to inform the design process throughout.”

Part One

GLASS AND WALL SYSTEM DEFINITIONS
Source: National Glass Association

GLASS

Float glass
A sheet of glass made by floating molten glass on a bed of molten tin. Float glass is made of common raw materials: sand, soda ash, dolomite, limestone, and salt cake. During the float glass process, other materials may be used to add color, refine, or adjust the properties of the glass.

Annealed glass
Float glass that is slowly cooled at a specific rate to strengthen it and make it less brittle. When broken, it fractures into large, jagged pieces.

Heat-strengthened glass
Made by uniformly heating annealed glass, then cooling it at a specific rate. This type of glass is about twice as strong as regular annealed glass of the same size and thickness. When broken, it fractures into large, jagged pieces, similar to annealed glass.

Tempered glass
Made by heating annealed glass, then cooling it rapidly using air quenching (blowing air uniformly onto both surfaces at the same time). A lite of tempered glass is twice as strong as heatstrengthened glass and four times as strong as annealed glass. When broken, it shatters into cube-shaped particles, reducing the likelihood of serious injury or impact.

Laminated glass
Made by placing an interlayer, often polyvinyl butyral (PVB), between two or more glass lites, which are then fused under heat and pressure in an autoclave. When laminated glass breaks, the glass particles adhere to the interlayer, making it a suitable material for safety glazing applications.

Insulating glass
Insulating glass units are made from two or more lites of glass separated by a sealed airspace. IG units reduce heat loss in the summer and heat gain in the winter. They also reduce the level of noise transmission. Each surface of an IG unit is designated by a number: No. 1 faces the exterior; No. 2 is inside the first lite; No. 3 faces the No. 2 surface; and No. 4 faces the interior.

Low-E glass
Has a very thin, invisible metallic coating that minimizes the amount of ultraviolet and infrared light (or heat) that can pass through the glass, without compromising the amount of visible light that is transmitted. Low-E coatings are typically applied to surfaces No. 2 and No. 3 of insulating glass units.

METAL SYSTEMS

Curtain wall
An exterior, non-load bearing wall system that utilizes glass, and vertical and horizontal mullions acting as structural members to transfer wind and gravity forces to the building structure. The system is anchored to, and supported by, the structural members of the building. There are two types of curtain wall systems: stick and unitized.

Stick curtain wall
A curtain wall system in which the mullions are installed first, and then the glass panels are inserted into the mullion framing in the field.

Unitized curtain wall
A factory-assembled and -glazed curtain wall system. The mullions are fabricated with the glass panels in place, and then erected as individual panels.

Window wall
Factory-glazed window and door units installed between the floor slabs of multiple-story buildings. When the floor slab edges are covered on the exterior with aluminum slab covers, the resulting appearance is that of a curtain wall.

Punched windows
Individual window units are “punched” into a building elevation and surrounded by non-fenestration façade materials.

Butt-joint glazing
A system in which the glass is not supported by mullions, but instead joined together by means of structural silicone, mechanical fastener or structural glazing tape.

Point-supported glass
A glass wall system without mullions. Individual lites of glass are attached to the building structure with fittings connected through holes in the glass.

Storefront
A non-residential system of doors and windows mulled as a composite structure; typically designed for high-use/ abuse and strength. Popular in low-rise buildings, storefronts are typically installed in ground-floor applications and anchored between the slabs.

Thermal break, thermal barrier
A component made of material of relatively low thermal conductivity, which is inserted between two components having high thermal conductivity, in order to reduce heat transfer.

ARCHITECTURAL FINISHES
Source: Linetec

Anodize
Anodizing is the process of electrochemically controlling, accelerating and enhancing oxidation of an aluminum substrate. The anodizing process is an integral part of the substrate, producing an oxide film that is uniform, hard, and protects the rest of the aluminum substrate from deterioration.

Organic coatings
A factory applied, thin film layer containing resin, binder and pigments that is applied to the surface of an object to provide protection and a decorative organic coating.


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Project Overview
Hunt Tower

Hunt Tower in Rogers, Arkansas, is a 10-story-tall, 235,000-square-foot Class A office building that features more than 80,000 square feet of curtain wall. The architect was Core Architects; the general contractor, Crossland Construction; and the glazing contractor, ACE Glass.

The project’s curtain wall is the aluminum, unitized 1600 System 2 from Kawneer Co. It is butt glazed vertically or horizontally on some elevations. The system includes 12-inch-deep pressure bar covers for aesthetics and to provide shading on some elevations. The glass is high-performance 1-inch insulating glass with PPG Industries' Solarcool Solar Gray coating on the No. 2 surface over clear with PPG Solarban 60 on the No. 3. Tristar Glass fabricated the glass. The project also features 40,000 square feet of the APS-WCE 175RS dryset/rain screen panel system. The system utilizes custom 2 1/2-inch reveals between large panels and two colors of prismatic paint.

In addition to the façade, the project features pointsupported exterior glass canopies and glass balcony railings. C.R. Laurence Co. supplied the spider fittings for the canopies and its heavy glass shoes and cap for the rails.

Part Two

PERFORMANCE AND DAYLIGHTING

GLASS AND GLAZING PERFORMANCE VALUES
Source: National Fenestration Rating Council

U-factor
U-factor measures how well a product prevents heat from escaping a home or building. U-factor ratings generally fall between 0.20 and 1.20. The lower the U-factor, the better a product is at keeping heat in. U-factor is particularly important during the winter heating season. The NFRC label displays U-factor in U.S. units. Labels on products sold in markets outside the United States may display U-factor in metric units.

SHGC
Solar Heat Gain Coefficient (SHGC) measures how well a product blocks heat from the sun. SHGC is expressed as a number between 0 and 1. The lower the SHGC, the better a product is at blocking unwanted heat gain. Blocking solar heat gain is particularly important during the summer cooling season.

VT
Visible Transmittance (VT) measures how much light comes through a product. VT is expressed as a number between 0 and 1. The higher the VT, the higher the potential for daylighting.

AL
Air Leakage (AL) measures how much outside air comes into a home or building through a product. AL rates typically fall in a range between 0.1 and 0.3. The lower the AL, the better a product is at keeping air out. AL is an optional rating, and manufacturers can choose not to include it on their labels. The NFRC label displays AL in U.S. units. Labels on products sold in markets outside the United States may display AL in metric units.

CR
Condensation Resistance (CR) measures how well a product resists the formation of condensation. CR is expressed as a number between 1 and 100. The higher the number, the better a product is able to resist condensation. CR is an optional rating, and manufacturers can choose not to include it on their NFRC labels.

DAYLIGHTING CONSIDERATIONS
Source: “The Facts about Windows & Daylighting,” from the National Fenestration Rating Council

The following are some issues that a design professional must consider when utilizing daylight. Seek the assistance of an expert consultant for more detailed information.

  • Remember that fenestration systems must have a source of daylight to be effective and that the fenestration must be able to transmit the visible light desired.
  • Automated daylight lighting controls = energy savings.
  • Modify daylighting needs to meet specific tasks (glare).
  • Consider light shelves to help distribute daylight and provide shading.
  • Incorporate indoor features to increase exposure to daylighting.
  • Consider the LSG index, or a “visible light to solar heat gain ratio.” References to this index typically recommend an LSG of 1.25 or greater.


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Project Overview
Sylvester Greenwood Academy

The Sylvester Greenwood Academy & LPS Richmond Charter High School in Richmond, California, features a range of glass, glazing and fenestration products that maximize daylight and thermal performance benefits. The school was designed by HMC Architects; and C A Lentini Design. The general contractor was Lathrop Construction; and the glazing contractor was AHC Glass.

The project features insulating, laminated glass with Cardinal Glass Industries’ 366 LoE in a range of thermally broken systems. Oldcastle BuildingEnvelope supplied its Reliance thermally broken curtain wall system, and the thermally broken 3000 and 6000 series storefront systems. Mon-Ray Inc. supplied the windows—the DeVAC 400 Series single frame aluminum windows, and 600 Series dual frame aluminum window, with non-structural thermobarrier. The school also features custom sunshades from ASCA Inc.; triple-glazed double hip skylights from Sunoptics; metal skylights from Crystalite Inc.; and tubular skylights from Solatube. AHC Glass also designed and installed custom shadow boxes. On the interior, the school also features fire-rated glass, FireLite Plus Premium from Technical Glass Products.

Part Three

FREQUENTLY ASKED QUESTIONS

Where can I get information about glass performance values?

Glass fabricators can provide center-of-glass performance values. From a window and wall system perspective, the system manufacturer commonly provides values. Full-system/product values, including all aspects of the framing and edge of glass, can be calculated and modeled using the center of glass and framing values.
National Fenestration Rating Council

What’s more appropriate for my project, unitized curtain wall or stick curtain wall? (See Table 1)

“Stick” curtain wall systems are shipped in pieces for field-fabrication or -assembly. All stick curtain walls are field-glazed. Frame assembly requires the use of either:

  1. “shear blocks” to connect vertical and horizontal framing elements, or
  2. “screw-spline” construction, in which assembly fasteners feed through holes in interlocking vertical stacking mullions into extruded races in horizontals.

Performance of any field-assembled or field-glazed curtain wall is only as good as the field workmanship allows. This is limited by variables, such as weather, access, and job site dirt and dust. Many critical seals are necessary, even in systems that are designed to drain rain penetration from the system back to the exterior.

To accomplish as many of these critical seals as possible in controlled factory conditions, and to minimize dependence on scarce and expensive field labor, “unitized” curtain wall systems have been developed.

Unitized curtain walls are factory-assembled and factory-glazed, then shipped to the job site in units that are typically one lite wide by one floor tall. Only one unit-to-unit splice—usually a silicone sheet or patch—needs to be field-sealed, and only one anchor per mullion needs to be attached to the face or to the top of the floor slab. Interlocking, unitized curtain wall frame members are weather-stripped to seal to one another, both horizontally and vertically. This accommodates thermal expansion and contraction, inter-story differential movement, concrete creep, column foreshortening, and/or seismic movement. Most unitized curtain wall systems are installed in a sequential manner around each floor level, moving from the bottom to the top of the building.
— Steve Fronek, vice president, technical sales, Wausau Window and Wall Systems

Table 1: Stick or Unitized Curtain Wall System Criteria
Source: Wausau Window & Wall Systems
 
Selection criteria Stick Curtain wall Unitized Curtain wall
Project size Small Large
Wall configuration Complex (Many changes in plane, e.g. soffits, corners, etc.) Repetitive (Large expanses of flat wall)
Joint pattern Random Uniform horizontal sill line
Glazing Field Factory
Inter-story movements Very limited Inter-locking frames accommodate movements
Quality control Subject to site variables (Both environment and equipment) Controlled factory conditions
Modification Can be cut-to-fit in the field Pre-engineered
Sealing Subject to site variables Minimal field sealing
Field labor cost High (Many parts to track and assemble) Low
Field labor duration Slow Fast (Often setting 75 square feet or more per unit)
Access and safety Exterior access required Set from the interior (Exterior optional)

How can I incorporate operable windows into façade systems for natural ventilation and improved indoor air quality?

We recommend the use of sub-framing in order to incorporate zero sightline vents into the curtain wall, window wall and storefront systems. In some cases we recommend [architects] use master frame options to limit bulky sightlines inherent in most window systems.
—Steve Schohan, marketing and communications manager, YKK AP America

Are there windows available from U.S. manufacturers that support high-performance, zero-energy building (ZEB) goals?

When approaching near-ZEB performance, it is inadvisable to rely on traditional paradigms regarding system interaction. In most commercial buildings, cooling loads dominate. Hence, in typical commercial construction, triple glazing is often deemed unnecessary and U-factor considered a secondary design parameter. However, for ZEBs in some climates and occupancies, changes in U-factor can have a greater percentage impact on overall energy consumption: The overall building energy consumption is much less to begin with, making the same U-factor-driven change in heating load more significant.

A small group of U.S. manufacturers offer operable and fixed windows exhibiting European-benchmark thermal performance, but with clean styling and narrow sightlines attuned to U.S. architectural preferences. Innovative composite framing design creates AAMA-AW Class architectural windows with best-in-class performance up to R6 (U-factor ~0.17 BTU/hr/sqft.°F). No-compromise product selection is made possible by combinations of aluminum extrusions and engineered polymers.
—Steve Fronek, vice president, technical sales, Wausau Window and Wall Systems

How can we incorporate more bent glass into our projects?

There is a lot of interest in bent glass design, whether it’s used extensively or just an accent. Now architects and designers have the option of specifying bent or flat glass applications on one project—both with the latest in coating technology—so the glass offers the best performance with the best coating, while presenting a nice, uniform appearance.
—Brian Schulz, commercial product manager, Guardian Industries Corp.

What is the better coating for a coastal application, fluoropolymer paint (often referred to as Kynar) or anodize?

As a prominent part of the building’s exterior, the coated aluminum adds color and design to the project; this coating also protects the building from unsympathetic surroundings. When selecting a coating that will be required to stand up to harsh coastal or corrosive environments select either:

  1. the highest-performing organic paint coating that meets the AAMA 2605-13 specification, or
  2. a Class I anodize coating that meets AAMA 611-14.

The American Architectural Manufacturers Association continues to set the highest standard for architectural coatings, especially in a coastal or highly corrosive environment. It is essential in any highly corrosive environment, such as a seacoast, that a regularly scheduled cleaning and maintenance routine is in place.

If there is any question that the cleaning and maintenance may lag, Linetec’s suggestion to the architect is to select a 70 percent fluoropolymer coating, pretreated with chrome phosphate, along with an inhibitive chrome-rich primer. If not properly maintained, anodize can be more susceptible to long-time salt deposits that are left to pond on the finish.
— Tammy Schroeder, senior marketing specialist, Linetec

How do I know if a wall system will meet structural load requirements in an application?

Unfortunately, there’s no quick answer. We need to review drawings and evaluate each condition separately. Factors such as design pressures, modular widths and heights, anchor points, and mullion heights must all be considered. It’s really a diagnostic/prescriptive process; a matter of specifying the appropriate system once we’ve addressed the application-specific performance requirements.
— George Heflin, U.S. Aluminum, sales manager, C.R. Laurence Co.

Katy Devlin is editor for Glass Magazine. E-mail Katy at kdevlin@glass.org.