In addition to specifying glass for its aesthetic and energy-related performance, architects, design professionals and specifiers must consider and account for many factors as early as possible in the design and specification process.
Among the main considerations are:
Safety—Appropriate safety glazing materials, such as tempered or laminated glass, must be specified where required by codes, or when dictated by design judgment based on the intended application.
Thermal Stress—Strengthened glass (heat-strengthened or tempered) may be required to resist thermally induced stresses in the specified glass. These stresses are caused by a number of design factors, including the glass type, shading patterns, indoor shading devices, etc., and if not considered, can and do lead to glass breakage. Thermally induced glass breakage is recognized and well understood in the glass industry. We have long offered procedures to help design professionals evaluate the risk and specify strengthened glass when required. You may wish to review our Technical Document TD-109: “Thermal Stress Update” for further information. In addtion, we offer a computerized thermal stress analysis program.
Wind and Snow Loads—The appropriate glass thickness and type (annealed, heat-strengthened or tempered) must be specified to resist wind and/or snow loads for the application. The current industry-accepted procedure for determining the load resistance of glass is ASTM E1300 “Standard Design Practice for Determining Load Resistance of Glass in Buildings.” You may wish to review our Technical Document, TD-134: “Designing Glass to Resist Wind and Snow Loads,” in the Technical Bulletins section of the website, for a brief tutorial on the use of ASTM E1300. A computerized version of the ASTM E1300 procedure is also available for purchase from the Standards Design Group, Inc. For Vitro Certified Network™ customers, a computerized version of ASTM E1300-02 is available on the website.
Surface Orientation—When darker tinted glass (such as Graylite® II glass) is specified, it is critical that the glass be fabricated and glazed with consistent surface orientation in order to achieve consistency of appearance. You may wish to review our Technical Document TD-122: “Surface Orientation of Low Light Transmittance Glasses,” in the Technical Documents section of the website for more information.
Aesthetics and Mock-Up—Vitro Architectural Glass (formerly PPG glass) offers a broad selection of clear and tinted glass products that can be used as stand-alone products for their own inherent beauty and performance, or combined to create deeper and richer hues and improved performance. Many additional aesthetic, environmentally friendly and energy control solutions can be achieved by including a high-performance glass coating in the design, such as a visibly reflective coating, a non-reflective low emissivity coating or one of our many non-reflective solar control low-emissivity coatings. The broadest product selection in North America can further be combined with custom fabrication using multiple glass lites, ceramic frits, laminates, etc., which can lead to an almost infinite number of installed glass products. Today’s individualistic design concepts can truly be achieved when utilizing our glass technology. The ultimate glass solution for your project marries the preferred aesthetic to enhance the building façade with the many other design considerations of performance, safety, wind/snow loads, thermal stress, etc. Once all the design considerations have been appropriately addressed, we strongly recommend the viewing of a full-size mock-up, preferably at the job site, prior to making final design decisions.
Availability—Available software, such as the LBNL Window program, permits users to simulate practically unlimited combinations of glass, gas cavity gap and gas fills in insulating glass units. Use the Construct Tool to design custom insulating glass units for your next project. It is the design professional’s responsibility to ensure that specified products are available and that they are available in the desired sizes.
For a complete discussion of all the issues and design considerations related to the fabrication, installation and performance of large insulating glass units (IGUs), please review TD-140 Large Insulating Glass Units.
Fabrication—Large IGUs can be tough to handle during fabrication. Large pieces of glass are simply more difficult to manage through the fabrication process than smaller ones and tend to have more issues with spacers and seal ruptures, distortion and damage within the sealed air cavity.
Weight—Large glass units are heavy, and weight increases the chance of damage during fabrication, handling and glazing.
Field Issues—A large IGU can be extremely unwieldy, and that means the people working with it have to be extra careful to prevent it from breaking or damaging the edges and from being exposed to temperature extremes, which can also cause breakage.
Glazing—Large IGUs require a glazing system that is specifically designed for these types of units, because the system needs to be able to support the heavy weight of the glass. Cost and budget come into play because different glazings have different costs, and you must weigh the cost of a particular glazing versus the benefit it provides.
Heat-Treating—With large IGUs, chances are that the glass will need heat-treating. However, while heat-treating makes glass more resistant to wind loads and thermal stress, it also increases the chance of distortion.
For an overview of the factors that should be considered in the glass design/specification process, download our Glass Guidelines brochure.
For the complete list of glass design/specification factors and related Glass Technical Documents, download the Glass Design Guidelines technical document.