Glass has been used as material in construction for thousands of years, and over the centuries the place of glass in the way we build has changed dramatically. This is largely down to the fact that the technology available to us has developed, and the ways we produce glass have evolved.
There are many types of glass available to contractors and architects, and understanding their properties and uses is an invaluable asset in the design & construction process. Here are some of the most commonly used types:
1. Tempered Glass
A familiar and instantly recognisable type of glazing, tempered glass is an industry standard in everything from car windscreens to the freezer doors in supermarkets.
Four times stronger than standard annealed glass, tempered glass is made using a heating and quenching process that strengthens the panels, increasing their resistance to impacts and pressure. This ensures that if they do shatter the glass explodes into comparatively harmless chunks, rather than razor-sharp shards.
Tempered glass usually only breaks at around 24,000 psi, compared to the resistance of 6,000 psi or so of standard glass. Due its superior strength, tempered glass is nearly always the go-to when safety is a concern. It’s also often a necessity due to local construction laws, regulations, and requirements.
Tempered glass is used in almost every area of both residential and commercial construction, and is particularly common in doors, windows, floors, and ceiling panels. It’s also used in everything from laptop and computer screens to protective eyewear, and any structure with specific safety regulations.
Due to the way it’s produced and the compounds from which it’s comprised, glass is often full of impurities. While these don’t affect the structural quality of the material, they can have a visual impact on the overall aesthetic, which is usually more noticeable the thicker it is, and the more panels that are placed together. Many of us will be familiar with the ‘greenish’ hue that glass often takes on -- but few are aware that this is due to the presence of iron.
In projects where the visual clarity of the glass is important, low-iron glazing can be used, which offers a much clearer, ‘whiter’ finish. This type of glass is made from silica, and while many in the industry will be familiar with ‘clear glass’ as an option, low-iron glass actually offers a purer result.
This type of glazing is usually used in projects that are specifically aesthetic in their design. These can include eye-catching pieces such as fish tanks and observation panels, and also in luxury or ultra-modern installations including frameless glass extensions.
3. Laminated/Shatterproof Glass
While the use of tempered glass is standard practice throughout the industry, laminated glazing offers a literal additional layer of strength. Tempered glass is safer than annealed, but it still shatters, and when structural security as well as safety is the primary concern in a construction project, laminated glass is often a better choice.
Laminated glass is made by two (or more) panes of glass being sandwiched together with a layer of polyvinyl butyral (PVB) between them. After heat and pressure is applied, the panels become fused, and upon impact the glass will remain in one piece rather than shattering. Laminated glazing products can be made from a variety of treated glass panels, including tempered and heat-strengthened solutions.
Laminated glass is often used in situations in which glass provides a structurally integral function. This can include things such as aquarium tanks, or installations in which the glass provides a surface for people to walk on such as glass staircase, a glass floor panel, or a bridge.
4. Heat-strengthened Glass
While it might initially appear that heat-strengthening and tempering are the same thing, these two techniques offer different properties to the glass panels in question, and as a result make them more suitable for specific construction situations.
While tempered glass usually has a surface compression of a minimum of 10,000 psi, heat-strengthened glazing normally only requires a compression of between 3,500 to 7500 psi. This might initially make it seem that due to its superior strength, tempered glass is the obvious option, but due to the way heat-strengthened glass is treated, it exhibits a number of different properties.
Specifically, when heat-strengthened glass breaks, it acts more closely to untreated annealed glass - in that it cracks into larger pieces, and usually remains held in place in its frame, preventing it from falling and hurting anyone.
The characteristics of heat-strengthened glass make it suitable for projects in which wind and temperature resistance are significant factors, but where full tempering is not required. For this reason, heat-strengthened glass is often chosen when full regulation safety glass is not required, but a weaker annealed glass panel wouldn’t provide suitable resistance.
Heat-treated glass panels are often used in laminated solutions, with projects including things such as curtain wall façades for buildings, when human impact safety situations aren’t a requirement.
5. Fire-Rated Glass
While glass is never a fire deterrent in and of itself, fire-rated glass panels are available when building regulations have specific criteria for fire protection. Fire-rated glass plays a role in ‘compartmentation’: ensuring a fire remains contained, and helping to prevent smoke and flames from spreading to different parts of a building or room.
Fire-rated glass is put through a battery of rigorous tests to receive its rating, which is awarded in the form of a time increment, determined by how long the installation survives in testing. Panels are subjected to intense heat in the wall of a furnace, and are then subjected to ‘thermal shock’ with a cold water hose.
Fire-rated glass comes in a wide variety of formats, from the institutionally recognisable wire mesh panels to the more modern wall units, and it’s possible to treat all kinds of installations to resist fire. While standard glazing usually fails at anything around 250F, fire-rated glazing can resist temperatures in excess of 1600F, with a rating of anything from 20 minutes to 3 hours.
Fire regulations play a part in all kinds of buildings and spaces, and often stipulate the fire-rating requirements for glazing solutions in specific parts of a building. Usually, the spaces which require the highest ratings are close or integral to exit routes, such as walkways or corridors which are required for exterior access. In these spaces, glass that is able to divert smoke and fire away from the path of people exiting the building is usually mandatory.
6. Switchable Glass
Switchable glass, sometimes referred to as ‘smart glass’ or ‘electrochromic glass’, is a relatively modern addition to the pantheon of glazing materials, and allows a user to change the opacity of the panel electronically. Through the manipulation of ‘liquid crystal molecules’ inside the frame, it’s possible to turn a glass panel from opaque to crystal clear - and back again - at the flick of a switch.
Smart glass panels are made from two panes of glass with a film layer of liquid crystal molecules sandwiched between them. The pane is wired to an electrical current that, when switched on, lines the molecules up perfectly to let light pass through unhindered, turning the glass completely clear. When the current is switched off, the molecules scatter and start refracting light all over the place - returning the glass to its default, opaque state.
The primary uses for switchable glass are for privacy and economisation of space. Switchable glass essentially mitigates the need for blinds or shutters to reduce ‘solar gain’ from windows (which occurs when the sun warms or overheats a room through uncovered windows, doors etc.), meaning windowsills and the space immediately in front of a window are left free.
They also provide a practical and easy way to improve privacy in a variety of commercial and residential settings. As such, they are often installed in bathroom and toilet windows, or meeting rooms for offices.
7. Low-e glass
As previously mentioned, one of the biggest considerations with many glass panels is the amount of heat they transfer into an interior space. Low emissivity (low-e) glass includes a microscopically thin clear film that reflects heat, and was developed to reduce the amount of UV and infrared light that passes through the glazing. This essentially reflects interior heat back into the room, and prevents additional heat from the sun from getting in - maintaining the interior climate without the need for air conditioning.
Low-e glass is predominantly used in modern residential and commercial builds, and can reduce the monetary and environmental cost of maintaining an interior climate through things such as air conditioning. Low-e glass is also useful in installations such as glazed extensions; during hot days, the sun can turn these spaces into ovens rather than living environments, and low-e glass mitigates this issue.