The Fenestration Glossary

TERM	MEANING
vent	the operating portion of a window that swings or projects in or out.
vent unit	A window or door that opens, to provide ventilation.
vent unit	A window or door unit that opens or operates.
vinyl	A plastic material used by some window for cladding or entire window units.
visible light transmittance	The percentage of visible light (380 to 760 nanometers) that is transmitted through glazing. Visible light transmittance is affected by special coatings and the number of panes of glass or film in an insulating glass unit.
warm edge spacers	Insulating spacers used to seal panes of glass in the manufacture of insulated glass units -- edge conductivity is lessened for improved window energy performance and reduced condensation problems. Warm edge spacers include Swiggle Seal^® by Tremco Ltd., and HeatSeal* from Southwall Technologies Inc.
wave length selective	"Intelligent" coatings such as Low E2 and Heat Mirror allow for glazing combinations to permit selective gain or shielding of the sun's heat, while letting in visible light.
weather stripping	Thin sections of material used to prevent air leakage around operable windows and doors -- usually foam gasketing, metal strips, or vinyl.
weatherstripping	A material or device used to seal the openings, gaps or cracks of venting window and door units to prevent water and air infiltration.
wedge glazing	a flexible, continuous gasket that ensures a high compression seal between the glass and glazing bead by applying pressure.
weep slot	an opening cut into a window sill and/or sash rail to allow water to drain to the exterior.
wind load	the amount of pressure exerted by the wind on a window or door generally expressed in pounds per square foot (psf).
windload	Force exerted on a surface by moving air.
window size.	always expressed as width first, then height
windowpane divider	See muntin.
wire glass	1/4" clear or obscure glass having a layer of diamond or square pattern wire mesh embedded in the glass lite.
XUV Fading Protection	A trademark of Southwall Technologies Inc. referring to Heat Mirror's ability to block 99.5% of damaging radiation passing through residential glazing (a standard dualpane blocks only 42%).
"XO" sliding window	"O" indicates fixed sash = left sash slides and right sash is fixed.
"XX" sliding window	"X" indicates moving sash = both sash operate.