Argon gas
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.
Astragal
The center member of a double door, which is
attached to the fixed or inactive door panel.
Awning window
A window unit in which the bottom of the sash
swings outward.
Bay window
A composite of three windows, usually made up
of a large center unit and two flanking units
at 30-,45- or 90- degree angles to the wall.
Block frame window
Used when replacing the wood sash of an old
double hung wood window.
Bow window
A composite of four or more window units in a
radial or bow formation.
Brickmold
A type of external casing which frames
windows and doors.
Casement window
A window unit in which the single sash cranks
outward, to the right or left.
Casing
Molding of various widths, thickness and
shapes applied to the framework of window and
door units.
Check rail
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.
Circlehead
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.
Cladding
Any material locked to the outside faces of
doors and windows to provide a durable, low-maintenance
exterior surface.
Clerestory window
A venting or fixed window above other windows
or doors on an upper outside wall of a room.
Cottage double-hung
A double-hung window in which the upper sash
is shorter than the lower sash.
Dormer
A space which protrudes from the roof of a
house, usually including one or more windows.
Double-hung window
A window unit that has two operable sashes
which move vertically in the frame.
Drip cap
A molding placed on the top of the head
brickmold or casing of a window frame.
Double or dual glazing
Use of two panes of glass in a window to
increase energy efficiency and provide other
performance benefits.
Extrusion
A form produced by forcing material through a
die. Most window frames are clad with
extruded vinyl or aluminum.
Fenestration
An architectural term referring to the
arrangement of windows in a wall. From the
Latin word, "fenestra," meaning
window.
Fixed window
Non-venting or non-operable window. Also
known as picture window.
Flashing
A thin strip of metal or synthetic material
that diverts water away from a window or
skylight.
Flush Fin
A replacement window with flush fin is used
when replacing an existing aluminum sliding
window. This is the most commonly used
replacement window type.
Foam Spacer
Foam material placed in the airspace of the
insulating glass in a window to enhance the
appearance and improve the performance of the
window.
Frame
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.
Glazing
Glass in a window or door; the act or process
of fitting with glass.
Glazing bead
A plastic or wood strip applied to the window
sash around the perimeter of the glass.
Glazing stop
The part of the sash or door panel which
holds the glass in place.
Grille
A term referring to windowpane dividers or
muntins, usually a type of assembly which may
be detached for cleaning.
Head
The main horizontal member forming the top of
the window or door frame.
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.
Hopper
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.
Jalousie window
Louver blades open to maximize airflow
through opening.
Jamb
The main vertical members forming the sides
of a window or door frame.
Jamb liner
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.
Lift
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.
Light shaft
An insulated shaft built to direct the light
from a roof window or skylight through the
attic to the room below.
Low-E glass
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.
Masonry opening
The space in a masonry wall left open for
windows or door.
Mortise
A slot or rectangular cavity cut into a piece
of wood to receive another part.
Mortise-and-tenon
A strong wood joint made by fitting together
a mortise in one board and a matching
projecting member (tenon) in the other.
Mullion
A wood or metal part used to structurally
join two window or door units.
Muntin
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.
Muntin Bar
Any small bar that divides a windows glass.
Also called a grille or windowpane divider.
Nail-on
Windows with nail-on frames are for new
construction.
Palladian window
A large, arch-top window flanked by smaller
windows on each side.
Panel
Usually refers to the separate panel or
panels in a door frame.
Parting stop
In a double-hung window, a strip of wood
applied to the jamb to separate the sash.
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.
Picture
Non-venting or non-operable window. Also
known as a fixed window.
Rail
The top and bottom horizontal members of the
framework of a window sash.
Rough opening
The framed opening in a wall into which a
window or door unit is to be installed.
R-Value
Resistance to thermal transfer or heat flow.
Higher R-value numbers indicate greater
insulating value.
Pane
A framed sheet of glass within a window.
Sash
A single assembly of stiles and rails made
into a frame for holding glass.
Sash balance
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.
Sash cord
In double-hung windows, the rope or chain
which attaches the sash to the counter
balance.
Sash lift
A protruding handle screwed to the inside
bottom rail of the lower sash on a double-hung
window.
Sash weights
In older double-hung windows, the concealed
cast-iron weights which are used to
counterbalance the sash.
Seat board
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.
Shims
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.
Sidelights
Narrow fixed units mulled or joined to door
units to give a more open appearance.
Sill
The main horizontal member forming the bottom
of the frame of a window or door.
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.
Single glazing
Use of single panes of glass in a window. Not
as energy-efficient as double glazing.
Single-hung
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.
Solar gain
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.
Stile
The main vertical members of the framework of
a sash.
Stool
An interior trim piece on a window which
extends the sill and acts as a narrow shelf.
Stop
A molding used to hold, position or separate
window parts.
Tempered glass
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.
Tenon
A rectangular projection cut out of a piece
of wood for insertion into a mortise.
Thermal break
The addition of a thermal insulating material
between two thermally conductive materials.
Transom
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 muntins.
U-value
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.
Unison lock
A casement locking system which secures the
window at two locking points by operation of
one handle.
Vapor barrier
A watertight material used to prevent the
passage of moisture into or through floors,
walls and ceilings.
Vent Unit
A window or door unit that opens or operates.
Vinyl
A plastic material used for cladding or
entire window units.
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.
Windload
Force exerted on a surface by moving air.
