Low-emissivity (Low-E) consists of a thin layer of metal oxide applied to the exterior face of the interior glazing in a double-glazed window. This coating allows sunlight to pass through, but blocks heat from escaping. A double-glazed low-E window provides similar insulation value to that of a triple-glazed unit, but costs less and weighs less. Low-E glazing filters out the suns ultraviolet (UV) rays, which can fade furnishings; and can reduce condensation on the window by keeping the indoor surface of the glass and frame warmer.
Inert gas fills are another innovation in window technology. Air is replaced with argon or krypton, between the panes of glass in a sealed unit. Inert gases have a higher insulating value than air because they are denser and have lower thermal conductivity, resulting in lower heat transmission between the panes of glass. Argon is the most commonly used gas due to its availability and low cost. Gas fills are a cost-effective upgrade over conventional air-filled glazings.
It is possible to get different coloured glazings to reduce solar heating and provide glare control. This technique is normally only seen in commercial or multi-residential highrise buildings. Films can be purchased to reduce glare from the sun, although glare can also be reduced through plantings outdoors, window awnings or shutters. Tinted films should be applied by a qualified contractor, as the application process requires some skill and special tools.
Sash
Windows come either fixed or operable (openable). Fixed windows do not open. Operable windows have a sash, which is a unit assembly of stiles and rails for holding the glass that moves when the window opens. They are available in a variety of sliding or hinged models. The sash can be made of wood, vinyl, metal or fiberglass and should make a tight seal with the frame when the window is closed. However, if the seal is too tight, the operable portion of the window may be difficult to operate.
Hinged models:
Casement:
Hinged on one side and swings open like a door. This design provides the best seal and has the lowest air leakage for a window that opens.
Awning:
Hinged at the top and opens out from the bottom. With an effective seal, this design minimizes air infiltration.
Hopper:
Hinged at the bottom and opens in or out from the top. An effective seal minimizes air infiltration.
Sliding models:
Horizontal sliders: Consist of two sashes, one or both of which slide horizontally in the frame. They are the least energy-efficient of the window types listed here, and the most prone to air and water leaks.
Single-hung windows: include one fixed sash (usually the top one) and one that moves up and down in the frame.
Double-hung windows: include offset upper and lower sashes, which can both move up and down in the frame. Both the singleand double- hung windows are not as energy-efficient as awning or casement windows, but their appearance may be more appropriate to the style of the house, especially in the case of older homes.
Tilt-and-turn (also called dual-action) windows: Swing from the side or pivot from the middle. Others pivot from both the bottom (like a hopper) and the side (like a casement). This allows for cleaning the outside of the window from the inside of the house and can be a valuable feature if a window is in a location where its difficult to get at from the outside. Be sure to have an effective weather seal for this type of window.
Spacer bars:
These appear around the perimeter of the sealed glazing unit to provide uniform separation between the panes of glass in multiple-paned windows. Spacer bars are typically made of aluminum, but spacers made of less conductive materials are now available. A high-performance/warmedge spacer can increase the energy efficiency of a window, provided that the frame is made of insulating materials (warm-edge spacers are less effective on metal-framed windows).
Spacers incorporate a dessicant that absorbs moisture from the trapped air in the space between the glass preventing fogging and condensation. Should your window fog, it means the seal is broken.
Casing:
This consists of the moldings that surround the window and cover the frame.
Hardware:
The hardware used in an operating window may include hinges, latches, cranks or levers. For security, some windows may have locks. The crescent-shaped locks are standard on many single- and double-hung windows.
Weatherstripping:
Weatherstripping is a component of an operable window, and provides a seal between the window-frame and the operable sash. It is used to prevent air leakage, and the better the weatherstripping, the better the window performance. There are two categories of design:
Wiper or Brush-type seals (sometimes called mohair) are more common in sliding windows, and wear out more quickly due to the type of window operation. They are also more likely to be used for exterior weather seals, and can tear easily if the window is opened when the seals are embedded in ice or frost.
Compression seals (sometimes called bulb) are also more fragile in cold weather, and can crack if the seal wall is too thin or the window is operated during very cold weather.
Weatherstripping is generally the most vulnerable component in an operable window, as it receives the most wear and tear. The seals should be checked annually for signs of wear or damage, and replaced as necessary.
