Figure 1. A cross section of a vinyl window frame with two panes of glass.
The window frame is the portion of the window that holds the glazing and sits between the glazing and the wall of the building when installed. The frame can be fairly simple in a non-operable window to very complex with numerous moving parts in an operable, multi-pane window. Overall, the main function of a frame is to hold the panes of the window in place—with the aid of spacers—and hold the window into the wall of a building.
Taking into account the frame as well as the glazing when choosing a window is vitally important in ensuring that the energy efficiency of the window is suitable. Looking at the U-values of windows along with their frames can provide a more complete idea of how well a window will insulate. In addition, the choice of the right window frame, especially a modern window frame, can cut air infiltration in a home down to nearly zero by covering cracks and creating a good seal. This can cut up to 40% off of heating and cooling bills.
Window frames can be made out of a wide variety of materials, and can be made solely out of one material or a composite of numerous materials. The most common frame types are wood, vinyl, aluminum, and more recently fiberglass frames. Composite frames include vinyl or aluminum clad wood products, wood clad vinyl products and other combinations to meet a variety of demands.
Modern window frames can be made from a variety of materials, each with their own benefits and drawbacks. The four main materials used in building window frames are:
- Wood: Wood frames have been used extensively in window frame construction for their warm look, insulating properties, and the ability to paint them to refresh how the frames look. Wood frames are the most common choice for frames as they can be painted a solid colour or stained and sealed. However, compared to vinyl and fiberglass frames, wood frames require more maintenance including regular sealing, staining, and painting. Although affordable, they may not provide the highest levels of insulation and are prone to cracking, in turn letting untreated air and water into the home.
- Fiberglass: Fiberglass window frames are beneficial as they are extremely strong, low maintenance, look traditional, and are paintable window frame options. These frames are composed of glass fibers and resin, and are very well suited for environments with drastically changing temperatures as the frames are resistant to expansion and contraction due to weather changes. These frames are desirable as they replicate the look and feel of wood without swelling, rotting, or warping and they are more energy efficient than wood frames. However, fiberglass frames are significantly more expensive than wooden frames.
- Vinyl: Vinyl frames are a newer type of frame, made primarily of polyvinyl chloride or PVC. These frames are durable, extremely energy efficient, not susceptible to corrosion, and are essentially maintenance-free. Different vinyl composites that contain different additives can be used to give the frame different qualities. The addition of titanium dioxide makes the vinyl frames more heat resistant, for example. Vinyl frames are the least expensive of all material options, but their lack of maintenance and good insulating qualities also make vinyl frames an appealing option.
- Aluminum: Aluminum window frames are valued for their slim profile but durability, along with their low maintenance and strength. Due to their lightweight construction and strength, aluminum window frames are able to be configured in a variety of ways. This makes them beneficial for multi-panel systems or large windows. However, aluminum frames are not recommended in wet areas or areas that have high levels of salty water and air due to their corrosion. In addition, the welded joints can weaken over time, resulting in cracking and breaking. However, compared to vinyl, fiberglass, and wood frames aluminum frames are the least energy efficient as they conduct heat well. To reduce this, some companies have equipped aluminum frames with thermal breaks that separate the interior and exterior surfaces of the frame to reduce heat transfer.
"Clad" frames are also a type of composite frame that are available. These frames consist of a vinyl or aluminum exterior and a wooden interior. These frames are more durable and require less maintenance, but are significantly more expensive than other frames.
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