Window Construction
Volume Discount Available. Call for details: (877) 747-5223.Technical Terms
The term “lite”, or “light”, refers to a glass pane, several of which may be used to construct the final window product. For example, a sash unit, consisting of at least one sliding glass component, is typically composed of two lites, while a fixed window is composed of one lite. The terms “single-light”, “double-light” etc. refer to the number of these glass panes in a window.
The lites in a window sash are divided horizontally and vertically by narrow strips of wood or metal called muntins. More substantial load bearing or structural vertical dividers are called mullions, with the corresponding horizontal dividers referred to as transoms.
In the United States, the term replacement window means a framed window designed to slip inside the original window frame from the inside after the old sashes are removed.
The U.S., the term new construction window means a window with a nailing fin designed to be inserted into a rough opening from the outside before applying siding and inside trim. A nailing fin is a projection on the outer frame of the window in the same plane as the glazing, which overlaps the prepared opening, and can thus be ‘nailed’ into place.
A beam over the top of a window is known as the lintel or transom, while a beam below the bottom of a window is known as the sill plate or window sill.
In the US, the NFRC Window Label lists the following terms:
- Thermal transmittance (U-factor). Best values are around U-0.15 (equal to 0.8 W/m2/K).
- Solar heat gain coefficient (SHGC) (ratio of solar heat (infrared) passing through the glass to incident solar heat)
- Visible transmittance (VT) (ratio of transmitted visible light divided by incident visible light)
- Air Leakage (AL) (Measured in cubic foot per minute per linear foot of crack between sash and frame)
- Condensation Resistance (CR) (Measured between 1 and 100. The higher the number, the higher the resistance of the formation of condensation.)
Windows can be a significant source of heat transfer. Therefore, insulated glazing units consist of two or more panes to reduce the transfer of heat.
Latest technologies for window manufacturing introduce a new vinyl systems free of steel with much better thermal insulation performance. To allow a steel elimination from the U-PVC window, new systems adopt a direct gluing of glass plates to the PVC frame. That is innovative engineering solution to prevent worst plastic property-temperature expansion and make a new unit consisted of glass and window frame.
Grids or Muntins
These are the pieces of framing that separate a larger window into smaller panes. In older windows, large panes of glass were quite expensive, so muntins allowed smaller panes to fill a larger space. In modern windows, light-colored muntins still provide a useful function by reflecting some of the light going through the window, making the window itself a source of diffuse light (instead of just the surfaces and objects illuminated within the room). By increasing the indirect illumination of surfaces near the window, muntins tend to brighten the area immediately around a window and reduce the contrast of shadows within the room.
Glazing and Filling
Low-emissivity coated panes reduce heat transfer by radiation, which, depending on which surface is coated, helps prevent heat loss (in cold climates) or heat gains (in warm climates).
High thermal resistance can be obtained by evacuating or filling the insulated glazing units with gases such as argon or krypton, which reduces conductive heat transfer due to their low thermal conductivity. Performance of such units depends on good window seals and meticulous frame construction to prevent entry of air and loss of efficiency.
Modern double-pane and triple-pane windows often include one or more low-e coatings to reduce the window’s U-factor (its insulation value, specifically its rate of heat loss). In general, soft-coat low-e coatings tend to result in a lower solar heat gain coefficient (SHGC) than hard-coat low-e coatings.
Modern windows are usually glazed with one large sheet of glass per sash, while windows in the past were glazed with multiple panes separated by “glazing bars”, or “muntins”, due to the unavailability of large sheets of glass. Today, glazing bars tend to be decorative, separating windows into small panes of glass even though larger panes of glass are available, generally in a pattern dictated by the architectural style at use. Glazing bars are typically wooden, but occasionally lead glazing bars soldered in place are used for more intricate glazing patterns.
Windows and the Sun
Sun Incidence Angle
Historically, windows are designed with surfaces parallel to vertical building walls. Such a design allows considerable solar light and heat penetration due to the most commonly occurring incidence of sun angles. In passive solar building design, an extended eave is typically used to control the amount of solar light and heat entering the window(s).
An alternate method would be to calculate a more optimum angle for mounting windows which accounts for summer sun load minimization, with consideration of the actual latitude of the particular building. An example where this process has been implemented is the Dakin Building, Brisbane, California; much of the fenestration has been designed to reflect summer heat load and assist in preventing summer interior over-illumination and glare, by designing window canting to achieve a near 45 degree angle.
Solar window
Photovoltaïc windows not only provide a clear view and illuminate rooms, but also use sunlight to efficiently help generate electricity for the building. In most cases, translucent photovoltaïc cells are used.
Window Coverings
A window covering is a shading or screening device that can be used for multiple purposes. For example, some window coverings are used to control solar heat gain and glare. Typically, there are external shading devices and internal shading devices. Low-e window film is a low-cost alternative to window replacement to transform existing poorly-insulating windows into energy-efficient windows.
For high-rise buildings, smart glass can be used as an alternative.
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