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Personal: Residential

Fenestration Products –
Components of Windows and Skylights

Frame and Sash Materials

A window consists of a glazed unit, a frame and a sash. The glazed unit fits into the sash, and the frame holds the sash. Frames and sashes are manufactured from a variety of materials and combinations of these materials.

Good quality windows and skylights can be made of a variety of materials, each with different characteristics:

  • Aluminum is strong and durable, requires little maintenance and resists warping. However, aluminum frames and sashes must be designed with significant thermal breaks to reduce heat loss by conduction.
  • Fibreglass offers excellent thermal performance, is durable and requires minimal maintenance. Hollow sections of the frame and sash may be filled with foam insulation to further reduce heat loss.
  • Vinyl provides good thermal performance and is easy to maintain. Large units may need reinforcement to increase their strength, and some reinforcing materials can increase conductive heat loss. Hollow sections of vinyl frames can be filled with foam insulation.
  • Solid wood has good insulating value and structural strength but requires protection from the weather, either through regular painting or staining or the use of low-maintenance, factory-applied claddings and finishes.
  • Combination frames and sashes are constructed of two or more materials, to take advantage of the best features of each material.
  • Composite frames and sashes are constructed of materials that have been blended so that the virtues of two or more materials are present in a single product.

Windows, doors and skylights can be compared by their energy performance and airtightness


Glazing is the generic term for the transparent material – usually glass – in a window, a door with window insert, or a skylight. These products may be single-glazed (one pane of glass), double-glazed (two panes) or triple-glazed (three panes).

Figure 11

The principal benefit of multiple glazing is that air, which is a good insulator, is trapped and sealed between the layers of glass. In Canada, all homes should have at least double-glazed windows mounted in an insulating glazed unit. In many regions, it may be worth the expense to add a third layer of glazing to existing windows. Reduced heat loss and higher interior glass temperatures will result in increased comfort; in addition, condensation and noise will be decreased.

Most manufacturers now offer the option of a low-emissivity (low-e) coating on their products – a thin, invisible metallic layer applied directly to the surface of the glass. The coating allows heat energy from the sun to enter the home while reflecting heat generated in the home back into the living space. This is an obvious benefit in winter.

Figure 24

In the summer, low-e coatings prevent heat that emanates from objects outside the home, such as pavement and buildings, from entering the living space and help to keep the interior cooler. A double-glazed window with low-e coating has an insulating value roughly equivalent to that of a standard triple-glazed window, but with less weight and often at a lower cost.

Figure 24 Figure 24

Self-Cleaning Glass

This is relatively new to the marketplace. A special coating is added to the exterior glass surface that will actually "shed" anything when it becomes wet. If the glass surface is in a place that doesn't allow it to become wet at all or frequently enough to clean the glass, a fine mist from your garden hose should be enough to start the "shedding" process. You should note, however, that the coating may scratch easily. The use of self-cleaning glass does not affect the energy efficiency of the window.

Gas Fills

Most manufacturers offer inert gas fill in glazed units as an option to increase thermal resistance and reduce heat loss. The gas used is odourless, colourless and non-toxic. Under normal conditions it will remain inside the glazed unit for many years. Argon is the most common gas, but krypton may also be used, especially in triple-glazed products.

Argon transmits heat poorly. In addition, because it is heavier than air, any heat it does capture becomes trapped between the window glazings.

Krypton gives slightly better performance than argon. As a result, the panes of glass can be closer together. Thus, less of this expensive gas is necessary, and multiple-pane systems are less likely to experience stress breakage.


Figure 13

Spacers are used to maintain a uniform separation between panes of glass in a glazed unit. Conventional spacers are made of hollow aluminum, a material that conducts energy easily and is a significant source of heat loss. Low-conductivity insulating spacers now available are made either from non-metallic materials, a combination of metallic and non-metallic materials (hybrid), or low-conductivity metal materials.

Low-conductivity spacers can improve the thermal performance of a low-e, gas-filled window, door with a window, or skylight by as much as 20 percent. These better spacers also keep the inside glass warmer around the edges, reducing thermal stresses on the glass and reducing the likelihood of condensation in cold weather.


Weatherstripping creates a seal at the moving joints of a window, a door with window insert, or a skylight to block rain and dust and to minimize air leakage. Compression seals are the most effective type of weatherstripping because they can be squeezed tightly between the moveable sash and the frame.

Figure 20

The design of some types of windows and doors makes it impossible to use compression seals. In this case, brush-type weatherstripping is used by the manufacturer to create a sliding seal.


Hardware includes the hinges, casement cranks, handles, locks, latch plates, etc., of operable units. Good quality hardware improves the thermal and structural performance of a window, door or skylight.

Changes in weather can affect the durability of the hardware. If you are having problems with broken or missing hardware, contact the manufacturer or dealer for replacement parts.