When selecting windows, energy-efficiency is a significant concern. High-efficiency windows can lower heating and cooling expenses. When specifying windows, glass type can determine energy-efficiency, while performance class designations identify the level best suited for the building. Since projects budgets allow for the purchase of windows only once, the wisest choice is not always based on price alone, but instead the long term performance.
Understanding Window Classes and Building Codes
The American Architectural Manufacturers Association (AAMA) standardizes window according to performance grades, distinguished by pounds per square foot (psf) of pressure (or wind loads) and the corresponding wind velocity:
- R class, 15 psf, designed for 77 mph wind speed.
- LC class, 25 psf, designed for 100 mph wind speed.
- CW class, 30 psf, designed for 109 mph window speed.
- AW class, 40 psf, designed for 126 mph window speed.
Choosing a window class depends on the application and performance required. Generally, The higher performance grades, the more capable the window is of withstanding greater operating force, deflection, and structural loading – meaning that the CW and AW class are usually selected for commercial projects.
FacilitiesNet.com also recommends knowing the applicable building code before choosing a window class. Requirements for structural stability typically cover window frame, glass, anchorage, and substrate attachment.
Understanding Window Glass Types
The type of glass may be dictated by building codes, along with the number of glazing options available to improve energy efficiency.
Annealed glass – raw glass that has not been heat-treated, is limited by code due to a tendency to break into large, sharp pieces.
Heat-strengthened glass – undergoes controlled heating and cooling to improve, is roughly twice as strong as annealed glass but still breaks into large, dangerous shards.
Tempered glass – undergoes controlled heating and then rapidly cooled, is roughly four times as strong as annealed. It is shatter-resistance and breaks into tiny pieces that are less likely to cause injury.
Dual-glazed windows have a relatively low U-value, which measures the window’s effectiveness in resisting heat conduction. Temperature transmission is reduced by introducing an airspace and creating a thermal break in the glass. Although triple glazing is also an option, dual-glazed is often the most cost-effective choice.
Low-e or Low-emissivity glass uses a thin coating to limit the amount of ultraviolet and infrared light that can pass through glass. Low-e glass is most cost-effective in moderate to colder climates, and in buildings with large areas of glass.
St. Cloud Window manufactures custom made, high-efficiency aluminum window and door products for new building construction, commercial window replacement, historic window replacement and projects where high-performance acoustic attenuation sets the standard. Not sure which high-efficiency windows are right for your project? View our full product line or contact us.
At St. Cloud Window we know every project begins with a challenge or an idea of what a building might be. We bring that vision to life with our distinctive design aesthetics, precision performance, and design-to-delivery support. Learn more about how our products can deliver on your design objectives and site requirements here. Then, check out our full line of historic replica and acoustic window products, and get in touch for more details about any of our high-performing commercial window products.