Glass is one of the most widely used building materials in architecture, design, and construction. With its unique structural properties, the material can be modified to produce different types of glass in construction.
Use and Structure of Architectural Glass
Glass is manufactured with different physical properties depending on what it will be used for. Several types of glass in construction vary based on safety, thermal performance, climate, and the visual appearance of the buildings. This post will explain the myriad of glass types so you can make an informed decision about what best suits your building needs.
Base glass consists of annealed float glass and ornamental glass. Float glass is the most basic glazing available internationally, making up to 90% of the base glass.
In the float glass production process, a hot steady layer of molten glass is discharged from a furnace into a huge shallow bath of molten tin. The glass floats and cools on the metal tin and expands to produce a flat surface. Rollers are laid across the glass to stretch and create a thinner glass surface.
Float glass has a maximum dimension of 6.0X3.2mm. The typical breaking strength of annealed float glass is 45N/mm2. Its standard thickness varies between 4,5,6,8,10,12,15,19 mm.
The float glass process produces high-quality structural glass for construction purposes.
Tempered Glass/Toughened Glass
Tempered glass is about 2.5 times stronger than standard glass of the same thickness in terms of physical or thermal shock. It is typically used for safety and strength. The glass is heated to a uniform temperature and instantly cooled to strengthen the glass. This makes the inner core of the glass stay fluid longer than the outer surface layer, which allows an equivalent amount of tensile prestress in the core and compressive prestress in the surface layer to be formed. The compressive prestress on the surface is preventing existing microcracks from growing thus making tempered glass stronger than normal glass. The common maximum dimension is 4.0 x 2.4m. The glass thickness is typically 4,5,6,8,10,12,15, or 19mm.
Tempered glass has a typical breaking strength of 120 N/mm2. When tempered glass breaks, it shatters into several non-cutting and fine pieces, avoiding the risk of injury.
Tempered glass is used commercially in structural glass applications where wind, snow, thermal or seismic loads are a threat. This type of glass is used for escalator side panels, balusters, handrails, and fire-resistant doors where strong support is needed. Likewise, it is also used in airport viewing areas.
Heat Strengthened Glass
Heat-strengthened glass is about 1.5 times stronger than float glass. It is heat treated in a similar way to tempered glass. However, the cooling process is less rapid compared to tempered glass. The typical thickness of this structural glass comes in 6,8,10, and 12 mm, and its common maximum dimension is 4.0 x 2.4m.
With a typical breaking strength of about 70 N/mm2, heat-strengthened glass has a breaking pattern with large pieces, which is favorable for some laminated glass applications where the post-breakage strength matters.
Heat-strengthened glass is used for structural glass applications in buildings where extra strength is needed to resist wind, snow, thermal and seismic loads. However, heat strengthened glass is not rated as safety glass, unless it is part of a laminated glass unit.
Laminated glass comprises two or more sheets of glass bonded together by interlayers of polyvinyl butyral (PVB) or ionoplast materials. Multiple layers of glass make even stronger glass panels. The excess of glass lites enhances the unit failure safety. The standard PVB thickness is 0.38, 0.76, and 1.52 mm. Their typical maximum dimension is 3.6 X 2.4 m.
Glass with Ceramic Frit
Ceramic frit is an enamel pattern on the glass surface. It comes in standard colors of the RAL system. The glass can be printed with common print patterns such as dots, holes, and stripes.
In order to apply the frit material to the glass surface, a porous polyester fabric screen (or silkscreen) is stretched on an aluminum frame. Sections of the screen are coated with a non-permeable material to create a stencil negative to the image being produced. This means the open spaces on the screen will develop the frit pattern on the glass surface. Following the frit application, the enamel gets burned in a furnace.
The ceramic frit pattern on the glass surface appears like a screen, acting as a partial or complete cover for privacy or hiding the background. Fritted glass is used for architectural glass walls, glass doors, partitions, stair rails, conference areas, and curtain walls.
Low Iron Glass
Low iron glass is a special float glass composed of raw materials cleaned of iron oxide which causes the greenish tint of regular clear float glass. The standard thickness falls between 6,8,10, and 12mm.
Low iron glass is used in façades and skylights, balustrades, glass floors, and all other applications, where the greenish tint of clear glass is not desirable. Moreover, structural glass fins are often made of low iron glass.
Body Tinted Glass
Body tinted glass is float glass formed from unique raw materials that create different colors of the glass. The typical dimension is 3.2 X 2.4 m, and the standard thickness ranges between 6,8,10,12 mm.
This glass reduces the transmitted solar radiation by absorption, thus reducing heat penetration into buildings and helping regulate the building’s temperature as well as limiting energy use. Body tinted glass adds aesthetics to the building with varying colors for stunning visual effects. This glass is typically used in combination with clear or low iron glass in offices, large buildings, and commercial spaces. It is excellent for facades, storefronts, interior design, and skylights.
Insulated glass units (IGU) have a lower thermal transmittance due to the enclosed interspace volume filled with air or argon. The U-value measures the thermal transmittance through the glass. The typical U-value for an air-filled IGU without any coating is about 3.0 W/m2*K.
Insulated glass is produced by sandwiching hollow aluminum or stainless spacer frames between two glass lites. The thickness of the spacer defines the interspace between the two lites. Butyl is used as the primary seal material between the spacer frame and the glass surfaces. Additionally, a secondary seal (silicone) encloses the spacer frame and bonds the glass edges together.
The IGU offers excellent thermal and sound insulation properties. Insulated glass units are used in residential buildings, hotels, colleges, hospitals, and offices. Moreover, it is used for buildings with high heating or cooling needs like airport cooling towers.
Insulated Glass with Low-E coatings
The thermal transmittance of IGUs can be lowered further using low-emittance (low-E) surface coatings which are microscopically thin, virtually invisible metal or metallic oxide layers. The glass acts like a one-way mirror to the interior space. It reflects most of the radiant heat coming from the interior side but transmits light from the exterior side. The typical U-value for an
air-filled IGU with low E coating is 1.6 – 1.9 W/m2*K. At the same time, the typical U-value for an argon-filled IGU with low E coating is 1.1 – 1.5 W/m2*K.
Insulated Glass with Solar Control Low-E coatings
The solar performance of IGUs can be improved using special solar control low-E surface coatings which act like a one-way mirror to the exterior space by reflecting most of the ultraviolet and infrared light but allowing visible light to pass. The solar heat gain coefficient measures the amount of solar energy transmitted through the IGU.
This type of glass is used in buildings to minimize heat transfer into homes, especially in warm climatic areas.
As evidenced by the production processes listed above, there are different types of architectural glass with varying properties that provide excellent performance and aesthetic appeal for architectural spaces.