Window technology has evolved over the years to the point where windows can be selected not only for their aesthetic qualities, but also for their performance abilities. For example, windows can be made from laminated glass that resists impact from flying debris in hurricanes, have special coatings that control the amount of heat gain and loss, or prevent water spots and dirt accumulation.

An NFRC label on the window will contain the information regarding the glazing features of a window - U-value, Solar Heat Gain Coefficient (SHGC), and Visible Light Transmittance (VT). Generally, the lower the U-value, the better the window performs at preventing heat loss (or gain in hot climates). U-value is equal to the inverse of R-value. SHGC is the fraction of sunlight, which is admitted through a window and released as heat indoors. It is expressed as a number between 0 and 1-- the higher the number, the more solar heat the window transmits. VT is the portion (between 0 and 1) of the sun’s visible light that is transmitted through a window.

Typically, distributors and retailers will stock windows with the glass that is recommended for given climates, but custom sizes and brands that require special order will allow a greater choice of glass features. The Efficient Windows Collaborative and Energy Star provide websites to aid in specifying the most efficient window for a given climate.

Building codes have long required laminated “safety” glass at hazardous locations like sliding glass and storm doors and windows adjacent to tubs. New on the building scene is glass laminated with composites that provide enough strength to allow windows to withstand high winds, projectiles, or even bullets. This impact-resistant glazing can reduce the risk of window failure and personal injury or property loss during tornadoes, hurricanes, and explosions. When struck, laminated glass may crack or shatter, but the glass fragments tend to adhere to a plastic layer and stay in place. In windows designed for high wind areas, a bonded interlayer is designed not to break under the stress of several projectile tests that model the force of airborne debris in high winds. The interior sheet of laminated glass is also adhered to a layer that will keep fragments in place.

Low-E and solar control low-E (also called spectrally selective) coatings can be used to boost the energy efficiency of windows. Low-E double pane windows, most common in cold and moderate climates, are more energy efficient than clear windows because the low-E coating reduces heat loss through the window.

Solar control glass, also called Low E2, is a good glass for hot climates because, in addition to improving the insulating ability of windows, it also limits solar heat gain by blocking passage of infrared and some ultraviolet rays. Solar control glass allows a higher level of visible light to pass through a window with less solar heat gain reduction than tinted window coatings.

Lastly, a new glass coating is available that sheds water more quickly than standard glass and resists water spotting and dirt accumulation. A thin, invisible layer of silicon dioxide, applied to a window’s exterior, makes the surface smoother than conventional glass and hydrophilic. Hydrophilic molecules attract water molecules and they blend together, making water a very good solvent in many situations. Therefore, rainwater collects in sheets, slides off glass quickly, and actually cleans the surface more readily than conventional glass.

One manufacturer combines the features of solar control glass with a hydrophilic coated surface called LoE2 Plus.

Specifications per Cardinal Glass, www.cardinalcorp.com/data/tsb/ig/IG05_05-08.pdf

(Lightning): In most U.S. climates, low-E coatings reduce heating costs associated with energy loss through windows by lowering the window’s U-value.

(Leaf): Compared to tinted windows, solar control windows allow more natural light to enter the home, thereby reducing the need for and energy used by artificial lighting.

(Shield): Impact-resistant windows can prevent damage and injury by preventing panes from shattering under impact.
Electrochromic windows can block the glare of the sun with the flip of a switch. Electrochromic windows are part of a new generation of technologies called switchable glazing-or "smart" windows. Switchable glazing can change the light transmittance, transparency, or shading of windows in response to an environmental signal such as sunlight, temperature or an electrical control. Electrochromic windows change from transparent to tinted by applying an electrical current. Potential uses for electrochromic technology include daylighting control, glare control, solar heat control, and fading protection in windows and skylights. By automatically controlling the amount of light and solar energy that can pass through the window, electrochromic windows can help save energy in residences.

A variety of electrochromic technologies and media have been developed. One type is darkened by applying a small electrical voltage to the windows and lightened by reversing the voltage. Light transmittance during operation varies from five to 80 percent. Once the change in tint has been initiated, the electrochromic glazing has "memory" and does not need constant voltage to maintain the tinting. Further, the film can be tuned to block certain wavelengths, such as infrared (heat) energy.

Another switchable technology, the liquid crystal suspended particle device (SPD), contains molecular particles suspended in a solution between plates of glass. In their natural state, the particles move randomly and collide, blocking the direct passage of light. When energized, the particles align rapidly and the glazing becomes transparent. This type of switchable glazing can block up to about 90 percent of light.

(Lightning): Switchable glazings such as electrochromic windows can reduce energy costs for cooling by reducing direct solar gains into the home during the summer. In some northern climates this benefit can make it possible to eliminate the use of mechanical air conditioning systems altogether.

(Leaf): The environmental benefits include the reduced use of energy and the reduced reliance on window coverings.
Today there are new window products available for those who are looking for an energy-efficient, water and air-tight window that will resist warping and fading.

Testing indicates that composite materials have excellent long-term durability. However, their use for window applications is relatively new; installation in housing started in the mid-1990s. Although relatively new to the market, fiberglass is an excellent green choice for window frames. Some Canadian manufacturers fill hollow fiberglass frames with urethane foam to increase R-value.
Entry doors should be chosen carefully since the serve both ornamental and protective purposes. Insulated fiberglass or steel entry doors are much more efficient than a solid wood door. Fiberglass doors have also proven to be much more resistant and can be manufactured to give realistic wood grain patterns.

Sliding glass doors are technically large windows and should be treated as such. It is crucial to ensure excellent weather-stripping between the doors in order to increase efficiency and minimize energy loss.