Window glass is more than just plain old glass

This article summarizes the growing list of available and developing glass options being offered by commercial and residential window manufacturers.

Note: Not all manufacturers offer the same products or options, so be sure to shop around to find what you are looking for. Also, some options may only be available for commercial applications only, as it may not be cost-effective for residential use.

The Technology

Advancements in window technology, have taken window selection for the home to a whole new level by providing options and solutions that can be applied on a per-room basis.

• Glass can be ordered in various thicknesses, strengths and hardness
• Special coatings can be added to glass to reflect, absorb and provide shade and privacy
• Special gasses can be added between the panes to increase a window's insulating properties
  
• Glass can be electrostatically charged and controlled to change its colour, shading and privacy
• Other technological glass advances continue to improve the properties of windows
  

Glazing

Glass panes

One of the shortcomings of glass is its relatively poor insulating qualities.

Window glazing refers to the glass framed within a window (IGU’s - insulated glass units). Multiple panes of glass with air (or gas as is used in today’s windows) spaces in between improve the insulating value of the window considerably.

In Canada, double-glazed glass has become the standard. However, triple-glazing and even quadruple-glazing windows are also available from most window manufacturers.

More is more energy efficient

Each additional pane of glass adds to the insulating value of the assembly, but it also reduces the visible light transmission and the solar heat gain coefficient. Adding a low-E coating to the surface of the double-pane unit will increase the energy performance. Adding a gas fill between the layers of glass will also improve energy efficiency.

Not all insulated glass windows are created equal, be sure to compare glass, frame and combined glass/frame ratings.

Spacers

Spacers separate panes of glass. Typically the older technologies utilize metal spacers which conduct heat and can encourage the formation of condensation (year-round) and ice crystals (winter).

Newer spacer technologies focus on providing durability, gas retention, and thermal performance, with the goal of keeping the edges of the window glass warmer inside the home through the reduction of, heat transfer.

There are several spacer technologies available, and each manufacturer will claim to have superior technology. When comparing windows, be sure to look at CR values and the overall performance of the window.

Super Spacer®

Warm edge spacer system that uses a high-performance acrylic adhesive and foam spacer along with a moisture vapour seal that provides a structural seal.

Intercept® spacer

Uses a one-piece, tin-plated or stainless steel, U-channel design that absorbs flexing when temperatures shift.

Swiggle® spacer system

The seal consists of an aluminium or stainless steel "swiggle" between a butyl rubber seal.

Aluminium spacer

One of the first materials used as a spacer because it was rigid, however creating sealant stress and stress cracks that ultimately lead to seal failure. If you are replacing old windows at this time, they most likely have aluminium spacers.

Gas Fills

Filling the space

Initially, multiple pane window spaces were filled with air or flushed with dehydrated nitrogen just before sealing. Through continuous testing and development window technologists discovered that air currents between the glass panes carry heat to the top of the window along the inner pane and settle down the outer pane into cold pools at the bottom.

Over time, manufacturers discovered that by filling the space between the glass with a less conductive slow-moving gas such as Argon, Krypton, and Xenon. These odourless, colourless & non-toxic gasses, minimize convection currents, reducing conduction through the gas and the overall heat transfer (lowering the U-factor) between the interior and exterior, thus improving the overall performance of the glazing.

Slow deterioration

Maintaining the long-term thermal performance of a window is always a concern, and many manufacturers have developed processes to seal in the gasses. But, testing has shown there is still a small breakdown in gas, less than 0.5% leakage per year in a highly ranked efficiency unit, that’s only about a 10% loss in total gas over a twenty-year period. Stability in gas life increases with the quality of the window design, materials used, and efficient assembly of the glazing unit seals.

Argon

Argon is the more widely used gas as it is readily available and much less expensive than krypton. The optimal spacing for an argon-filled unit is about ½ inch. In combination, argon gas and Low-E coatings will quickly yield energy savings exceeding their cost.

Krypton

Typically Krypton is used in applications where the total glazing unit thickness must be minimized, for example, ¼ inch. Its thermal properties are more efficient than Argon but more expensive. A mixture of krypton and argon gasses can be used to compromise cost and thermal performance.

Xenon

Xenon boosts a window’s thermal window U-value below those insulated with argon or krypton, improving the energy performance. But performance comes at a price. Xenon-insulation will usually cost much more than both argon and krypton, with just slightly better energy savings in return and is usually only used when a home has massive amounts of window siding.

Glass Coatings

Low Emissive Glass has a distinct microscopically thin layer of silver applied to the surface which acts to reduce the amount of heat that can flow through the glass. It reflects heat in both directions keeping heat out in the summer and in during the winter. Coated glass is available in several configurations to produce the desired balance between solar gain, light transmission and UV blocking. Talk to your local window consultant for an optional solution that’s right for you.

LoE 180 glass

• Highest Energy Star energy rating
• U-factor of 0.31
• Maximized solar gain of SHGC 0.68
• Allows for 79% light transmission
• Blocks 70% of damaging UV rays
• Reduces energy costs in the winter

LoE 272 glass

• Balanced option when the room is hot in summer and cold in winter
• U-factor of 0.30
• Maximized solar gain of SHGC 0.41
• Allows for 72% light transmission
• Blocks 84% of damaging UV rays
• A moderate solar gain in winter and controls heat in the summer

LoE 366 glass

• This is the best insulation option for our Ottawa climate
• U-factor of .29
• Keeps heat and sun out of the home in the summer and heating or air conditioning inside the home
• Maximized solar gain of SHGC 0.27
  
• Allows for 65% light transmission
  
• Blocks 95% of damaging UV ray
• Delivering an ideal balance of solar control and high visibility

Privacy

Window privacy can be managed at the glass through various options offered by many window dealers. By incorporating the privacy option into the glass, the buyer can neglect window treatments that require cleaning or cluttering of living spaces.

Textured glass

Many window manufacturers offer an assortment of obscure/textured glass that is used for light diffusion, decorative effects, and to provide privacy. There are 4-5 standard patterns, but many manufacturers offer more. Patterns are typically stamped into the glass.

Frosted glass

Frosted glass reduces visibility through the glass. It is typically applied through a sandblasting/masking process to the side of the glass that will be facing away from the inside of the home and can be distinguished by its white opaque frosting. By today's standards, it is typically only available in multi-pane glass units.

Integrated blinds

Dynamic windows have integrated insulating blinds between the panes that can be used for privacy as well as to reduce heat loss in winter and solar gain in summer.

Smart windows

Not offered by many window manufacturers, smart windows are a speciality product that is not readily available.

The glass has special coatings that react to natural light levels by increasing reflection or darkening or both. This smart function can be activated manually or programmed to control heat gain, and lighting, and add privacy.

ENERGY STAR qualified smart products are available but are qualified based on ratings achieved without using the smart features.

Tints

At times the sun, heat and peeping eyes can be very invasive and uncomfortable, especially if there are no external trees or hedges to filter them out. Glass tints are available in various colours and strengths to help make your home more private and comfortable.

Visual Transmittance (VT)

Tints can produce great results but like any glass treatment, they can have an effect on the amount of light (expressed as a number between 0 and 1) able to pass through a material without being reflected or absorbed.

High transmittance glass (larger unit of measurement) allows more light in and may help reduce the cost of electrical lighting, whereas glass with low transmittance may result in a slight increase in energy cost for lighting.

Marginal efficiency gain

Tinted glass absorbs and re-radiates light and solar energy reducing heat, brightness, and glare in the summer, but lose heat in the winter at the same rate as non-tinted windows.

Every change in colour or combination of different glass types affects visible transmittance, solar heat gain coefficient, reflectivity, and other properties. Glass manufacturers list these properties for every colour, thickness, and assembly of glass type they produce.

Daytime privacy

Tinting changes the colour of the window and can increase visual privacy during the day. However, at night the effect is reversed, and it is more difficult to see outdoors from the inside.

Tinted glass is available in a number of colour tints (grey, green, bronze & blue ). These colours are produced by adding metal oxides to float glass (untreated glass) during manufacture.

Security

If security is of prime concern, different types of processed glass will help protect your property, however, depending on your requirements the options could significantly increase the cost.

Glazing (glass panes)

The more panes of glass in a window, the more difficult it is to break for the purposes of forced entry into a home. Dual pane is now the standard set by most manufacturers, but triple and quadruple are also available from some manufacturers.

Laminated glass

Made by bonding one or two layers of glass with a layer of resin, commonly polyvinyl butyral (PVB). Produces a compact glass that holds in place rather than shattering when hit making it very difficult for burglars to get through.

Tempered glass

Tempered glass is about 5 times stronger than regular glass, the manufacturing process involves heating, high-pressure, and chemical treatment procedures that toughen the glass making it very difficult and loud to break.

Glass and Sound

Although it is not possible in today’s technology to create a totally soundproof glass window, there are several ways manufacturers can help reduce noise from coming into or out of the home. Factors that can affect the way sound travels through a window include the thickness of glass, the spacing distance between glass panes, the use of laminated glass, and the use of dissimilar glass thicknesses in multiple pane glass units.

More on windows and unwanted noise

Durability and Maintenance

The glass that is used in the manufacturing of windows has also evolved to address issues of scratching. With the introduction of lead (about 10%) and other substances in the mixture for glass (hard glass). Hard glass will not scratch easily whereas pure glass (soft glass) will. Note: the lead in glass is not considered dangerous, as it will not leach.

Although glass will get dirty, it won’t degrade or stain through sun exposure, chemicals or other surrounding environmental effects. Even dirt is not an issue with the self-cleaning glass option - a special coating that stops dirt particles from sticking to the glass - dirt can easily be washed away by rain or a garden hose. To reduce seasonal staining from condensation which can form both inside and outside your home try to get the most insulated glass as possible.

Because window glass may be coated on the outside surface of a glass unit, care should be taken to ensure it is not damaged.

More on cleaning windows
More on self-cleaning glass

Summary

Buying windows can be as easy, or as complicated as you want. It’s up to you as a homeowner to ensure that you purchase durability that will maximize comfort, security and cost-saving energy efficiency. It’s well worth doing a little homework and asking lots of questions. Keep in mind, depending on your desired outcome, each room in your home may require a different solution.

For more information, please talk to one of our window associates. Give us a call or send us a request through our contact page, we’d love to talk to you.