If you're considering replacing the windows in your home, the latest window craze is switching to triple-glazed, or triple-pane, windows.
In a triple-pane window, each sash contains three layers of glass. An air space is created between each layer with the use of spacers (usually aluminum), and then the unit as a whole is hermetically sealed to keep air and moisture outside. The idea is that the additional dead space between the pieces of glass will reduce noise and provide better insulation.
The standard rating for residential sound transmission is called the STC rating. While many factors affect the STC rating of a window—such as the thickness of the glass and the amount of space between separate pieces of glass—an MIT study suggests that all things being equal, “Triple glazing provides essentially the same noise reduction as double glazing.”
If you're really after noise reduction from your windows, asymmetrically glazing a dual-pane window will do a better job, and increases the STC rating more than triple-glazing. In asymmetric glazing, two pieces of glass of different thicknesses are used. In fact, if one of the pieces of glass is laminated acoustic glass (which consists of two or more pieces of glass bonded together with a laminate material), there is a significant reduction of sound transmission.
Insulation and Heat Values
Insulated windows are used in an attempt to maintain interior temperatures as cost-effectively as possible -- you don’t want to run the air conditioner all day in the summer, and you don't want to blast the heater for long periods in the winter. It's estimated that you can lose 20 to 30 percent or more of heat or cooling in your house through poorly insulated windows. Replacing windows can make good economic sense and add to your comfort level while indoors.
Manufacturers claim that triple-pane windows are 25 percent better on average than double-pane windows. When shopping for windows, pay attention to the U-factor and R-values, which are measures of the windows’ ability to block heat transfer to the outside. The National Fenestration Rating Council suggests that the U-factor provides a better overall indication of transmission than the R-value; the lower the U-factor, the better the window is at keeping heat inside.
Additionally, there is a measure called the Solar Heat Gain Coefficient (SHGC), which measures the amount of heat that a window blocks from direct sunlight. The lower the number, the more efficient the window is at blocking heat from the sun.
Two key considerations covered here are cost and comfort. Triple-glazed windows can reasonably be expected to cost roughly $100 more per average-sized window than a dual-glazed window. It's estimated that each window will save maybe 3 percent on annual heating bills, and much less in more temperate climates. So, on one hand, triple-pane windows may not be cost-effective depending upon your climate. On the other hand, improved efficiency will add to your comfort.
Other Considerations: Light, Framing, Installation, Security
Lighting is an important architectural consideration in choosing windows. Windows minimize solar heat gain with coatings called Low-E placed on one of the surfaces of the interior pieces of glass. Low-E coatings work by blocking the infrared or heat-producing rays of the sun.
Manufacturers claim that Low-E is also designed to maximize the amount of visible light a window lets in while blocking the heat from direct sunlight. However, some believe Low-E coatings on dual-glazed glass make both the rooms and triple-glazed glass noticeably darker.
It's not unusual to order windows with different coatings for different rooms, depending upon each room’s individual demands. However, the coatings add a slight, usually bluish-green tint to the glass, and if two windows with different coatings are side-by-side, the difference will be very noticeable.
An additional cost to consider is that of the frame. The least expensive triple-glazed window is a vinyl framed window. They are usually only available in minimal colors (white and almond). In today’s marketplace, vinyl frames are durable and insulate well, but their bulkiness is visible from both the inside and outside. However, most manufacturers offer a limited lifetime warranty and maintenance is minimal.
Some manufacturers offer fiberglass frames, which are extremely durable. They last a lifetime, are easy to maintain and are less bulky than vinyl. However, fiberglass can cost up to 50 percent more than vinyl. The chief benefit is that fiberglass frames are paintable. If you're unhappy with the standard colors offered by the manufacturer, you can always elect to have them painted. Or, if you are an ambitious DIYer—paint them yourself. Some manufacturers make vinyl and/or fiberglass-clad windows with a wood veneer on the inside, so that you can stain the wood for a traditional look, maintaining a low-maintenance durable exterior.
Triple-pane, wood-framed windows are the most expensive option, but at the same time, they offer the most traditional look. However, as with any wood product, they require regular maintenance.
Installation for a triple-pane window can be slightly more difficult than with a standard dual-pane because they're thicker and heavier because of the added layer. But its weight is less of an issue because quality window manufacturers install operating hardware that makes them easy to operate. Tilt windows, however, can be a bit of a problem when tilted to clean because the sash is significantly heavier.
Installation can be difficult given that the window frames are thicker, and should only be attempted by the most-experienced DIYer. Depending upon the width of your exterior walls, accommodations to the interior wall may be necessary, as installation may require building up the interior wall in some fashion to accommodate the window projection into the home.
Security, as you might expect, is increased with a triple-pane window, because the extra piece of glass adds additional strength to the window and an additional barrier from intrusion.