With so many different types of glazing out there, it’s sometimes hard to know which glass is best for your project. There are various thicknesses, energy performance enhancements, decorative films, and color tints.

But don’t let all those options boggle you down. Here’s a basic rundown of the main glass types… anything beyond this is usually left to the experts.

Here’s a basic rundown of the main glass types… anything beyond this is usually left to the experts.

In this article we discuss:

  • size considerations for window wall glazing
  • best types of glazing for thermal performance and safety
  • glass options for decorative and privacy applications
  • unique glass types with technological advancements

 

 

Size Matters When It Comes to Window Glazing

The most defining characteristic of window walls is the sheer size and span. Whether openings consist of a really large single window unit, or multiple units mulled together, glass can now be fabricated to full story heights (or larger) and wall to wall widths to form some very large openings.

The size of the individual window units is only limited by the fabrication capacity of the glass manufacturer. New technologies and fabrication capabilities have pushed the limits on glass size.

Some modern homes now showcase full floor to ceiling panels of glass that were once unthinkable.

These large window units can be very appealing, but they do come at a higher price. The larger the unit, the higher the price.

In speaking with various window manufacturers, many recommend staying below 50sf of glass per unit. Anything over that, costs start to increase significantly. In addition, very large pieces may limit the number of glass fabricators that can create the glass itself (which is another reason costs may be higher).

large glass windows
[Private House in London. Photo by Hufton + Crow.]

If you are considering large glass sizes, be sure to check with the window company to confirm they can manufacture your desired sizes. Keep in mind that large operable windows and doors are not only limited by glass fabrication capacities but also the window/door hardware. Hardware capacities comes into play when the weight and proportion of the unit get bigger and heavier.

More Layers = More Efficiency

Most window glazing these days are comprised of double- or triple-paned units. (Single paned windows are quickly becoming obsolete with the ever increasing thermal performance requirements of building codes.)

With multi-paned windows (2-,3-, even 4-layers of glass), the glass panels have an air- or gas-filled layer between the individual sheets of glass. The air- or gas-filled layer provides additional insulation and improves the thermal performance of the entire glass panel. These insulated glazing units are sometimes called IGUs for short. 

double paned glass

Most window wall manufacturers use double paned IGU’s as their standard window assembly. Again, with newer energy codes most single-paned windows aren’t efficient enough. If you are concerned with energy loads, you may want to consider triple-paned windows or selecting higher performing glass panels, which we descibe below.

The Best Type of Glass For Thermal Performance

Since windows don’t have a very good thermal performance compared to solid walls, many glass manufacturers are making strides in technological advances to make windows more appealing to the energy-driven and sustainability-conscious community.

Window companies now provide a range of options to improve window thermal performance – making windows more appealing to everyone.

Here are the most popular glazing options to improve thermal performance:

Low-Emissivity (Low-E) glass – glass with a special invisible coating that reflects and blocks out heat and minimizes UV rays from passing through the glass and fading furniture.

Reflective glass – glass that has been treated with a metallic coating to allow it to reflect heat and radiation rather than absorbing it.

Reflective glass reducing heat gain and reduce visible light transmission. There are two methods: color-tints and reflective films.

  • Color-tinted glass – glass with small additions of color (bronze, green, blue or gray) that help control solar heat gain by absorbing heat. The color is homogeneous throughout the glass and doesn’t affect the basic properties of the glass except for solar energy transmission.
  • Reflective films – a reflected film applied to one of the sides of the glass to reduce solar heat gain. It also reflects more light and can sometimes have a mirror effect.
reflective glass windows
[Hunsett Mill by ACME Architects. Photo by Cristobal Palma.]

Of these, low-e glass is the most typical on window wall project. Window wall manufacturers typically provide this glass as a standard for many of their window systems to help meet energy requirements of today’s codes. Reflective glass is an option with some window companies, but it’s more widely used in the commercial sector for curtain wall and storefront systems.

Safety Glazing Options For Window Walls

You also need to consider safety when designing a window wall system. Glass (when broken) is sharp. As a way to minimize hazards associated with potential glass breakage, tempered and laminated glazing options are available.

Tempered glass – a type of safety glass that is physically and thermally stronger than normal glass. When broken, it breaks into granular chunks instead of splintering into jagged shards or glass. The tempering process puts the outer surfaces into compression and the inner surfaces into tension. The granular chunks are less likely to cause injury. (Think of the side and rear windows of passenger vehicles.)
tempered glass window
Laminated glass – a type of safety glass that holds itself together when shattered because it has a special interlayer (kinda like a piece of tape) between the glass layers. (Think of the windshield of a car.)
laminated glass windows

Also, note that tempered glass is required by building codes for all window glass located close to the floor/grade, near swinging doors, stairs, wet areas, and areas that have higher chances of breakage for safety reasons.  Glass doors also need to be tempered. So you will most likely have some tempered glass on your project.

Decorative & Other Unique Glass Types 

In addition to performance and safety options for window glazing, there are also various window options for decorative applications, privacy, and other unique functional necessities.

These glass types are typically personal preferences and not standard or traditional window wall system, so you’ll have to request or inquire about these.

These options typically add cost to  your window package. Some are minimal increases like simple films or etching. Others are more intensive because they require additional technology applications.

Nonetheless, depending on your project, the location, performance, and behavior of your window walls are very important aspects of the project so considering how the glass behaves may be very important to you and your project goals and worth considering.

Here are a few:

  • Translucent glass – an effect achieved with sandblasting, acid etching or applying a film to the surface of the glass to make it less transparent for privacy or decorative reasons. Obviously the glass film is the more affordable option.
  • Self-Cleaning glass – glass with a special chemical coating that reacts with daylight to break down organic dirt, cleansing itself via daylight and rain.
translucent window glass][Hollywood Hill Residence by Griffin Enright Architects. [Photo courtesy Griffin Enright Architects.]

 

  • Bird-friendly glass – glass with a patterned, UV reflective coating making it visible to birds while remaining virtually transparent to the human eye.
  • Electrochromic privacy glass – glass that turns opaque or translucent with the flip of a switch (electrodes are applied to the inside of the glass unit that when an electric current runs through it, the ions react and move to reflect light) for privacy reasons

And there you have it… the most typical types of glazing available for window walls.

Many of the glazing characteristics mentioned above can be combined with others to achieve a combination of effects to meet your unique needs.

When designing a window wall, most windows will have double or triple-paned low-E glass (with tempering as required). This is fairly standard among window wall manufacturers. Anything above and beyond that will need to be confirmed with the specific window company for availability and cost implications.

Everyone’s window wall project is different and has different requirements it must meet so choosing the best type fo glazing for your project should be discussed with your design team and window wall manufacturer.

 

This article is part of our Window Wall Design Series. We’ve covered the basics of window wall types, their benefits, and inspiring projects so far. In the next article, we dig in and focus on what factors affect window wall durability. 

5 Things To Consider About Window Wall Quality and Durability >

What Type of Glazing Is Best For My Window Walls?