Windows can be a significant source of heat transfer. Insulated glazing units therefore consist of two or more panes to reduce the heat transfer.

Grids or Muntins

These are the decorative, usually wood pieces that separate a larger pane into smaller segments. The mutins are generally held to the window frame using a pin of some sort.

Frame and sash construction

Factory site in Berlin-Spindlersfeld: window with letter S for Spindler Frames and sashes can be made of the following materials:

* Vinyl and fiberglass frames perform well in accelerated weathering tests. Because vinyl is not as strong as other materials, some vinyl frames are reinforced with metal or composite materials to improve their structural strength.

** Modern metal window frames are typically separated by a thermal break made of a non-conducting material. This greatly increases thermal resistance, while retaining virtually all of the structural strength. Composites may combine materials to obtain aesthetics of one material with the functional benefits of another.

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 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.

Other construction details

Many windows have movable window coverings such as blinds or curtains to keep out light, provide additional insulation, or ensure privacy.

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

Solar windows not only provide a clear view and illuminate rooms, but also use sunlight to efficiently help generate electricity for the building.

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