Window Terms Glossary
Small honeycomb spaces within the sash and frame which help
to insulate and strengthen the window
The amount of air that passes between a window sash and frame.
In windows it is measured in terms of cubic feet or air per
minute, per square foot of area. The lower the number, the
less air the window lets pass through.
Latch mechanism on the interior face of the sash that retains
the window in a partially open position for ventilation.
A sloped extension from the frame that adds an aesthetically-pleasing
dimension to the exterior of the window.
Argon is a safe, odorless, colorless, non-toxic, non-flammable inert gas
that is commonly used in place of air between the glass panes of an
insulated Low-E glass unit to reduce temperature transfer.
The center member of a double door, which is attached to the fixed or
inactive door panel.
A window unit in which the bottom of the sash swings outward for
for holding vertically sliding sash in any desired position
through the use of a spring or weight to counterbalance the
weight of the sash.
A composite of three windows, usually made up of a large center fixed unit and
two flanking units at 30-,45- or 90- degree angles to the wall.
angled extension from the frame that adds an aesthetically-pleasing
dimension to the exterior of the window.
Block frame window
Used when replacing the wood sash of an old double hung wood window.
A composite of four or more window units in a radial or bow formation.
A small metal tube that is placed into an insulated unit's spacer to
equalize pressure differences. Breather tubes can allow moisture to enter
into the insulating unit. Mostly used in high altitude locations.
A type of external casing which frames windows and doors.
A rubber material that seals the glass to the spacer, creating
an airtight and watertight IG unit. Butyl has the lowest
gas permeability of all rubbers.
Lock and Keeper
mechanisms which pull the sash together when placed in the
hollow tubes which penetrate the spacer system of an insulating
glass unit. They allow pressure equalization between manufacturing
locations, shipping, and installation locations. Since the
insulating glass unit is not permanently sealed, the air space
cannot be filled with Argon gas.
A window unit in which the single sash cranks outward, to the right or
Molding of various widths, thickness and shapes applied to the framework
of window and door units.
of Glass U- and R-values
U- and R-values measured from the center of the glass to 2-1/2"
from the frame.
On a double-hung window, the bottom rail of the upper sash and the upper
rail of the lower sash, where the lock is mounted.
A generic term referring to any of a variety of window units with one or
more curved frame members, often used over another window or door opening.
Any material locked to the outside faces of doors and windows to provide a
durable, low-maintenance exterior surface.
A venting or fixed window above other windows or doors on an upper outside
wall of a room.
Condensation Resistance Factor
A measure of the effectiveness of a window or glazing system
to reduce the potential for condensation. The higher the
condensation resistance factor, the more efficient the window
and glazing system.
transfer from one material to another by direct contact.
transfer by currents that flow from a warm surface to a colder
A double-hung window in which the upper sash is shorter than the lower
arced extension from the frame that adds an aesthetically-pleasing
dimension to the exterior of the window.
A space which protrudes from the roof of a house, usually including one or
A window unit that has two operable sashes which move vertically in the
A molding placed on the top of the head brickmold or casing of a window
Double or dual glazing
Use of two panes of glass in a window to increase energy efficiency and provide other performance benefits.
A form produced by forcing material through a die. Most window frames are
clad with extruded vinyl or aluminum.
An architectural term referring to the arrangement of windows in a wall. From the Latin word, "fenestra,"
Non-venting or non-operable window. Also known as picture window.
A thin strip of metal or synthetic material that diverts water away from a
window or skylight.
A replacement window with flush fin is used when replacing an existing
aluminum sliding window. This is the most commonly used replacement window
Foam material placed in the airspace of the insulating glass in a window
to enhance the appearance and improve the performance of the window.
The enclosure in which window sash or door panels are mounted.
French hinged door
Hinged door(s) which have wider panel members around the glass.
French sliding door
A sliding door which has wider panel members around the glass, giving the
appearance of a French hinged door.
Glass in a window or door; the act or process of fitting with glass.
A plastic or wood strip applied to the window sash around the perimeter of the glass.
The part of the sash or door panel which holds the glass in place.
A term referring to windowpane dividers or muntins, usually a type of
assembly which may be detached for cleaning.
The main horizontal member forming the top of the window or door frame.
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 window unit in which the top of the sash swings inward.
Insulating glass (IG)
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.
Louver blades open to maximize airflow through opening.
The main vertical members forming the sides of a window or door frame.
In a modern double-hung window, the track installed inside the jambs on
which the window sashes slide.
Knocked down (KD)
Unassembled window or door unit.
A handle or grip installed on the bottom rail of the lower sash of a
double-hung window to make it easier to raise or lower the sash.
Light or lite
Glazing framed by muntins and/or sash in a window or door.
An insulated shaft built to direct the light from a roof window or skylight through the attic to the room below.
A common term used to refer to glass which has low emissivity due to a
film or metallic coating on the glass or suspended between the two
lights of glass to restrict the passage of radiant heat.
The space in a masonry wall left open for windows or door.
A slot or rectangular cavity cut into a piece of wood to receive another
A strong wood joint made by fitting together a mortise in one board and a matching projecting member (tenon)
in the other.
A wood or metal part used to structurally join two window or door units.
Applies to any short or light bar, either vertical or horizontal, used to
separate glass in a sash into multiple lights. Also called a windowpane
divider or a grille.
Any small bar that divides a windows glass. Also called a grille or
Windows with nail-on frames are for new construction.
A large, arch-top window flanked by smaller windows on each side.
Usually refers to the separate panel or panels in a door frame.
In a double-hung window, a strip of wood applied to the jamb to separate
Passive solar collector
Any glazed area in the walls or roof of a building pointed to the south
to take maximum advantage of the sun's heat without a mechanical (or
active) method of storage or distribution of the heat.
Non-venting or non-operable window. Also know as a fixed window.
The top and bottom horizontal members of the framework of a window sash.
The framed opening in a wall into which a window or door unit is to be
Resistance to thermal transfer or heat flow. Higher R-value numbers
indicate greater insulating value.
A framed sheet of glass within a window.
A single assembly of stiles and rails made into a frame for holding glass.
A system of weights, cords and/or coiled springs which assist in
raising double-hung sash and tend to keep the sash in any placed
position by counterbalancing the weight of the sash.
In double-hung windows, the rope or chain which attaches the sash to the
A protruding handle screwed to the inside bottom rail of the lower sash on
a double-hung window.
In older double-hung windows, the concealed cast-iron weights which are
used to counterbalance the sash.
A flat board cut to fit the contour of a bow or bay window and
installed between the sills and the flat wall surface, providing a seat
or shelf space.
Wood wedges (often wood shingles) used to secure the window or door
unit in the rough or masonry opening in a square, level and plumb
position during and after installation.
Narrow fixed units mulled or joined to door units to give a more open
The main horizontal member forming the bottom of the frame of a window or
Simulated divided light
A method of constructing windows in which muntins are affixed to the
inside and outside of a panel of insulating glass to simulate the look
of true divided light.
Use of single panes of glass in a window. Not as energy-efficient as
A double-hung type of window in which the top sash is fixed or inoperable.
Sloped Sill Adapter
Used to cover the gap between the old sloped sill window and the new
block frame window. It adapts a new window to the existing sloping sill.
The process of providing a net heat gain within a structure, over and
above the normal heat loss, by passive collection of the sun's heat
through windows and other glazed areas.
The main vertical members of the framework of a sash.
An interior trim piece on a window which extends the sill and acts as a
A molding used to hold, position or separate window parts.
Glass manufactured to withstand greater than normal forces on its surface.
When it breaks, it shatters into small pieces to reduce hazard. Standard
on all doors and large fixed windows.
A rectangular projection cut out of a piece of wood for insertion into a
The addition of a thermal insulating material between two thermally
A small window that fits over the top of a door or window, primarily for
additional light and aesthetic value.
True divided light
A term which refers to windows in which multiple individual panes of glass or lights are assembled in the sash using
Rate of heat flow-value through the complete heat barrier, from room air
to outside air. The lower the U-value, the better the insulating value.
A casement locking system which secures the window at two locking points by operation of one handle.
A watertight material used to prevent the passage of moisture into or through floors, walls and ceilings.
A window or door unit that opens or operates.
A plastic material used for cladding or entire window units.
A material or device used to seal the openings, gaps or cracks of venting
window and door units to prevent water and air infiltration.
Force exerted on a surface by moving air.
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