Friday, August 28, 2009

Windows technical terms

In insulated glass production, 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 USA, 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. Northern Virginia Replacement Windows are a framed windows in Northern Virginia. In Europe, replacement window usually means a complete window including a replacement outer frame.

The USA 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).

In the UK and Europe, windows in new-build houses are usually fixed with long screws into expanding plastic plugs in the brickwork. A gap of up to 13mm is left around all four sides, and filled with expanding polyurethane foam. This makes the window fixing weatherproof but allows for expansion due to heat.

A beam over the top of a window is known as the lintel or transom.

In the USA, the NRFC 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 (in cubic foot per minute per linear foot of crack between sash and frame)

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