Learning Resource

What is Insulating Glass Units?

Insulating Glass UnitsInsulating glass units, or IGUs, are designed to keep homes warmer in the winter and cooler in the summer.

Insulating glass units commonly consist of two (sometimes more) panes of glass separated by a spacer material and sealed together at the edge. The insulating airspace is filled with air or a noble gas, such as argon or krypton inside. Each glass pane has two surfaces, so typical double-paned insulating glass units have four surfaces.

What is Laminated Glass?

Laminated glass is produced by permanently bonding two pieces of glass together with a tough plastic interlayer (polyvinyl butyral) under heat and pressure. Once bonded together, the sandwich behaves as a single piece. The interlayer is invisible when viewed through the glass and with glass on either side, the finished lite is indistinguishable from plain glass when installed. Most often, laminated glass is produced from annealed glass, but heat strengthened or tempered can be used when special performance needs are present. The benefit of laminated glass is that if broken, glass fragments adhere to the plastic interlayer rather than falling free and potentially causing injury. Laminated annealed glass can be cut or drilled. Laminated glass is required in sloped glazing applications that exceed any of the following conditions:
The area of each pane (single glass) or unit (insulating glass) exceeds 16 square feet.
The highest point of the glass is greater than 12 feet above any walking surface or other accessible area. The nominal thickness of each pane exceeds 3/16 inch.

Laminated glass is highly effective in reducing noise thus improving Sound Transmission Ratings. The best design incorporates laminated glass in an insulated unit. The damping characteristics of the plastic interlayer combines with the attenuating characteristics of the air space of the IG unit to maximize sound reduction. Example: Two lites of 1/4″ laminated glass in an IG unit with a 1/2″ air space provide an STC rating of 42. This compares with two pieces of monolithic 1/4″ glass in an IG unit with a 1/2″ airspace the STC rating would be 35. Laminated glass eliminates 99.9% of ultraviolet rays, making it highly effective in protecting furnishings, displays, merchandise, etc. Standard laminated glass is 7/32″ with a .030 (approx. 1/32″) polyvinyl butyral layer.

What is Low-E Glass?

Low-E glass products give you year-round energy savings and comfort by helping manage the sun’s energy and the heating system energy in your home. Low-E glass products are coated with microscopically-thin, optically transparent layers of silver sandwiched between layers of antireflective metal oxide coatings. In the summer, Low-E glass products let in visible sunlight while blocking infrared and ultraviolet solar energy that drives up cooling costs and damages curtains, window treatments, carpeting and furnishings. And in the winter, Low-E glass products offer greater comfort and reduced heating costs by reflecting room-side heat back into the room. Emissivity is a measure of how much heat is emitted from an object by radiation. Heat is transferred to and from objects through three processes: conduction, convection, and radiation. For instance, on a hot night, heat will be conducted through a window from the outside, causing the inside pane to become warm.

Convection, or natural circulation, of the air in the room past the window will transfer some of that heat into the room. But the window will also radiate heat as infrared waves, which will warm objects throughout the room. This radiative heating is why you can feel the heat of a red-hot piece of metal (for instance, a heating element on an electric stove) from several feet away. Low-emissivity, or low-e, coatings are put on window panes to reduce the amount of heat they give off through radiation. In hot climates, where the outside of the window will typically be hotter than the inside, low-e coatings work best on the interior of the outside window pane. In cold climates, where the inside of the window is typically hotter than the outside, the low-e coatings work best on the inside window pane, on the side that faces toward the outside.

What is Obscure Glass?

Some obscure or pattern glass gets its pattern by going through rollers after the float glass process that have the pattern on the rollers. It adds privacy where window covering are impractical or undesirable (bathrooms, sidelights) and is available in various colors and texture patterns provide a translucent of semi-opaque effect. It may or not not be tempered.

Types of Obscure Glass

  • Gluechip – A fine etched pattern glass that is made by pouring an epoxy on the glass and letting it dry in a high humidity environment. The glue is then chipped away which removes portions of the glass.
  • Reed – A type of obscure with a vertical reed pattern.
  • Rain – A type of obscure with a rain pattern.

What is Tempered Glass?

The tempering process produces highly desirable conditions of induced stress which result in additional strength, resistance to thermal stress and impact resistance. Fully tempered glass must have a surface compression of 10,000 PSI (Annealed is below 3500 PSI) and heat strengthened must have a surface compression between 3,500 and 7,500 PSI. The basic principle employed in the heat treating process is to create an initial condition of surface and edge compression. The condition is achieved by first heating the glass, then cooling the surfaces rapidly. This leaves the center glass thickness relatively hot compared to the surfaces. As the center thickness then cools, it forces the surfaces and edges into compression.

Wind pressure, foreign object impact and thermal stresses or other applied loads must first overcome this compression before there is a possibility of breakage. In the heat treatment process the key procedure is application of a rapid air quench immediately upon withdrawal of hot (1200 degrees F) glass from the tempering furnace. The immediate and sustained application of an air quench produces the temper. A quenched condition becomes stable when the glass is reduced to a temperature of approximately 400-600 degrees F. Tempered glass is about 4 times stronger than annealed.

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