The Fenestration Glossary

TERM	MEANING
gasket	a rubber or plastic pliable material used to separate glazed glass and aluminum or vinyl.
glazing	Glass in a window or door; the act or process of fitting glass or panels into the sash or frame of the window.
glazing	The installation of glass into a window or door sash. Also refers to the type of glass used in the process.
glazing bead	a molding or stop around a window frame to hold the glass in place by pressure. A vinyl or wood strip, applied around the perimeter of the glass on the exterior of the window sash, for holding the glass in place.
glazing stop	The part of the sash or door panel which holds the glass in place.
greenhouse effect	The property of glass that permits the transmission of short-wave solar radiation, but is opaque to long-wave thermal radiation. The interior of a car heating up in direct sun illustrates the greenhouse effect.
grille	A term referring to windowpane dividers or muntins, usually a type of assembly which may be detached for cleaning.
grilles	Decorative inserts for windows or door glazing that add a traditional touch -- available as fixed or removable inserts, in wood, brass, or vinyl.
grilles-between-the glass	Aluminum bars in varying thicknesses and profiles sealed between insulating glass panels to simulate muntin bars.
gusset	a concealed, strong, right-angled shape used to reinforce mitered corners in tubular aluminum extrusions
head	The main horizontal member forming the top of the window or door frame.
head board	A flat board, cut to fit the contour of a Bow or Bay window, for installing between the head jambs and the flat wall surface to finish off the area which would normally be ceiling.
head expander	a u-shaped extrusion slipped over the frame head that, when pushed up, closes the gap above the window after window installation.
header	A horizontal framing member placed over the rough opening of a window to prevent the weight of wall or roof from resting on the window frame. A beam across the top of the rough opening for a window or door. Headers rest on jack studs and support the weight of the wall above the window unit. They are often constructed out of doubled 2x6’s, 2x10’s or 2x12’s.
heat fusion	(welding) method to join PVC frame and/or sash members by heating the cut ends, squeezing them together, and allowing the assembly to cool.
heat treating	the process where glass or aluminum extrusions are heated and cooled to make these materials harder and stronger.
hermetically sealed unit	an insulating glass unit that is sealed against moisture. The unit is made up of two lites of glass, separated by a roll-formed metal spacer tube (at the full perimeter) which contains a moisture and/or solvent absorbing material. The unit is then completely sealed, creating a moisture free air space.
hollow extrusion	an extrusion having an enclosed cavity within it.
hopper	A window unit in which the top of the sash swings inward.
IGCC	Insulating Glass Certification Council - directs a certification program of periodic accelerated laboratory testing and unannounced plant inspections to ensure sealed insulating glass performance is in conformance with ASTM E 774-88.
inside snap trim	used in retrofit work to cover the inside gap between the new window and the existing opening.
insolation	Incident solar radiation -- the total radiation striking an exposed surface.
Insulating Glass Unit (IGU)	A combination of two or more panes of glass with sealed air space(s) between panes -- dualpanes, tripanes, and quadpanes. Also referred to as thermopanes or sealed units.
Insulating glass(IG)	two pieces of glass spaced apart and hermetically sealed to form a unit with an air space between. Heat transmission through this type of glass may be as low as half that without such an air space. A combination of two or more panes of glass with a hermetically sealed air space between the panes of glass. This space may or may not be filled with an inert gas, such as argon. Two sheets of glass bonded together in a unit to enclose a captive air space. Units are constructed with a metal spacer inside the outer perimeter. The outer edges are sealed. Spacers contain desiccant material for absorbing and holding any remaining moisture in the air space.
insulation	A material with high resistance (high R-value or low U-value) that is used to retard heat flow. Air, Argon, or Krypton gas spaces between panes of glass provide insulation in IGUs.
integral mullion	a frame member trapped within the master frame to separate vents or fixed glass.
interior glazed	glass glazed from the interior of the building.
interlock	a design feature which enables sash to become engaged with one another when closed
internal gain	The heat produced in the interior of a dwelling from the operation of lights, appliances, etc.