A Basic Introductory of Glass and Best Practices of Glazing

A brief history, glass does not loan itself to the archaeological three age system of the history books, being stone, bronze and iron ages. This does not make glass any younger. For matter of fact natural glass formation can be said is as old as the world itself, formation from molten volcanic rock to lightning striking stone.

Different Types of Glass

Annealed or plate glass (sheet glass)
Laminated glass and
Tempered glass.

Picture of broken plate glass

Annealed Plate Glass:

Widely used in homes, for example windows. Plate glass is usually not used in storm doors, patio doors and shower enclosures. Plate Glass, in either residential or commercial properties, is not allowed for windows that are in a pathway or are below 24” from walking surface area doors. Other restricts on the usage of annealed plate glass are door side lites (the panel of glass on the two sides of a door), patio doors, and bathroom windows that are over and or near shower enclosures. All these must be tempered. Additionally, recent ANSI and ISO recommendation of any lite over 9 square feet must have safety glass.

Plate Glass Stress Cracks

A more positive point is that because the inner structure is immobile glass does not suffer from dynamic fatigue. Upon removal of stress glass returns unchanged by the exerted experience. A plate glass in a window exposed to wind over yeas does not fail because it is constantly being stressed by the wind. Stress cracks on plate glass or sudden breakage on tempered glass can happen due to different surface area temperature tension.

Glass lites partially shaded, and the other section is exposed to Ultra violet and infrared light, this effect internal stresses, cold portions of glass contracting and the heated portion expanding, thus causing a stress crack or sudden shattering of tempered glass. Other breakage to all glass is due to improper installation, glass abhors weight being distributed unevenly, rested directly on building masonry or metal without EPDM setting blocks (to absorb metal and building movement, contraction and expansion of substrate surface, edges should never touch the substrate without setting blocks).

Safety Glass

Have you ever stopped and thought why some perceivable fragile glass items are so durable? Those items are made are created using safety glass. Both Tempered and Laminated glass are considered safety glass. A common misconception is wired glass is considered safety glass. Wired glass is NOT safety glass. Interestingly, out of all the different types of glass, wired glass causes the most emergency room visits in the nation.

Importance of Annealed Plate Glass

Without plate glass both laminated glass, and tempered glass cannot be made, so everything leads back to plate glass, also known as float glass, due to the discovery and manufacturing practice pioneered by Pilkington.

Tempered Glass:

Shattered tempered glass

The tempering process consists of heating the glass to a temperature where it becomes flexible and then chilling it evenly and rapidly. The outer surface is chilled quicker than the inner glass. Because the core is trying to contract and the outer surfaces are already chilled the outer surface is being compressed while the core is under tension. The compression at the surface is pulling the glass together so any flaws are being closed rather than being free to open. It is only when the compressive strength is overcome that the glass will fail. Tempered glass is predictably 5 times stronger than annealed glass of the same thickness.

How Come Tempered Glass is Safety Glass?

Annealed plate glass breaks into shards, while tempered glass breaks into many small popcorn-like dull pieces. ANSI and ISO recommends any glass over 9 square feet should be safety tempered glass.

Tempered Glass Uses

Tempered glass uses are mentioned above, widely used in all high rise and commercial applications, in common everyday household and consumer good due to its heightened strength and its safety when break occurs. It can picked by bare hand without causing laceration. Examples of common, everyday uses of tempered glass include: cell phones, glass kettles, pyrex, and bathroom windows.

Common Tempered Household Items

Glass cups.
Glass pyrex dishes
Cell phones, tablets, and computers.
Passenger car windows and rear window. (not windshield)
Electric stove top with glass on it
Baking oven & Microwave glass

Laminated Glass:

Broken storefront glass

Ordinary window glass is brittle, breaking into long sharp pieces which can cause serious and sometimes fatal injuries. The principal feature of laminated safety glass is its performance under impact. Laminated glass absorbs the energy of the impact, resisting penetration. Although the glass may break, the glass fragments remain firmly bonded due to the PVB interlayer. In glass skylights, sunspaces, sloped glazing installations and curtain walling, there is always the possibility of breaking glass. Without the inclusion of laminated glass, this could result in injuries and safety issues with falling glass. This is why many building codes worldwide require laminated glass for overhead glazing.

Why should I use laminated glass?

Security: One of the biggest reason why laminated glass is used, is simply harder to break and therefore more secure. It can be manufactured to be bullet or bomb proof, it is used to protect drivers as by law all windshield need to be laminated glass to stop objects from entering into the vehicle.

Sound abatement: Laminated glass naturally absorbs sound due to the PVB sandwiched between the two glass that forms laminated glass.

Protection: In regions with adverse weather, where areas are prone to hurricanes, tornadoes hail, high winds causing large debris to hit the glass, the glass will break but stay intact due to the PVB film and stopping debris from penetrating the living space.

UV Light protection: Laminated glass blocks 95 percent of UV light.

When & where should I use laminated glass?