subject: Understanding Window Terminology [print this page] Familiarity with window terminology will assist you in buying the right type of window for your home. As windows generally last 20-25 years, new windows are not a frequent purchase item for homeowners. New technologies and performance standards have changed significantly over the past 20 years. Terminology commonly used in the window industry is presented in this fact sheet.
Components of a window
Windows consist of the following components: (see figure 1)
frame
sill
head
nailing flange
mullion
glazing
sash
stile
rail
hardware
Frame:
The horizontal and vertical portions that surround the sash and on which it is hung comprise the frame. Frames are usually made of the same materials as the sash. Window frames may be manufactured with or without nailing flanges. Frame and sash design and construction are important for both energy efficiency and appearance. Several materials are commonly used:
Wood frames have high insulating properties and can be painted or stained any colour. They require ongoing maintenance to prevent moisture damage. They are usually less expensive than frames made of other materials.
Clad wood frames have the advantage of woods natural insulating qualities, but they require less maintenance. The cladding is usually aluminum or vinyl, available in limited colours. Moisture problems can be reduced if the cladding is applied properly to the wood. If moisture gets trapped between the cladding and the wood, damage and rot can occur unseen.
Aluminum frames are strong and durable, but they readily conduct heat. To avoid heat loss and condensation, aluminum frames are required by the National Building Code of Canada to have a thermal barrier inside made from rigid foam, polyurethane or wood, to reduce heat transfer. While aluminum frames are durable and require little maintenance, they have poor insulating properties. Some aluminum frames have mitred joints in the corners, which can allow water to leak into the wall if the joints are not properly sealed or the seals fail.
Vinyl frames are available in two types.
1) Extruded vinyl frames incorporating internal air cavities
2) Reinforced inner structure of another materialwood or metal. Wood is preferable because it has better insulating qualities than metal.
Vinyl frames are very durable, and low maintenancethey can resist colour fading, moisture, termites, corrosion and air pollutants. The material can be easily shaped into the required dimensions. Vinyl windows provide good insulating properties even excellent, if the cavities in the sash and frame are insulated.
Fibreglass frames are relatively new. They are light, durable and strong, even in narrow sizes, they have excellent insulating qualities, and they do not expand and contract with heat and cold as much as other frames. They are also more expensive than other types of windows.
Glazing
The glazing: (or glass) can be a solid sheet of glass, or several panes divided by a mullion.A mullion is a secondary frame that holds the window-panes in the sash. Some glazings are made of tempered glass, to resist breakage, and some are made of laminated glass, which not only reduces breakage, but if the window does break, the glass shards will be too small to cause injury.
Double-glazed windows have two layers of glass separated with a spacer. It is the minimum standard allowed by the National Building Code of Canada. Air trapped between the glass layers provides some insulating value.
Triple-glazed windows have three layers of glass, or two layers with a low-emissivity (Low-E) film suspended between them. The additional layer and air space give triple glazing better insulation value than that provided by double glazing. It is a good choice where extremes in weather and temperature are the norm. Triple-glazed windows can help reduce sound transmission where outside noise is a problem, but because the sash is heavier it may be more difficult to operate than a double-glazed sash.
